hi @Lalading, you should be able to get 16x GPUs on a Z390. The M.2 slots are PCIe x4 (four lanes) so you can run a 4-port splitter with a M.2-to-PCIe x4 adapter. That will give you an extra 3 GPUs capacity.
[Apologies for the terrible photo]
Hi buddy, ultimately Watts = Volts x Amps so lowering any voltage should lower the power consumption (assuming the current does not automatically increase to compensate). Obviously there is a limit where lowering the voltages will impact performance or crash the GPU. I totally agree 650/1100 works universally well for the 6600s, I am just trying the squeeze every last drop of efficiency and maintain good uptime 
[re-written this bit, had quite a few beers, I confused myself] The TRM output (motd watch) shows the VDDC value it has “choosen” to use. I don’t know of a way to directly set this parameter (it can be lower than the HiveOS value). I “think” there is a correlation between Core Clock Mhz, SoC Freq and what value TRM chooses for VDDC. Lower the Core Clock Mhz or SocMhz and VDDC lowers. Its just a hunch, no hard evidence to support this yet. Strangely, what I did notice on the XFX and MSI 6600s was if you use Core=900 VDDC is higher than if you use Core=901. No idea why and I don’t have time to test it further atm, it may have been a fluke.
mate, you are 100% totally correct. All my 6600s are exactly the same. Thats the baseline.
Interestingly VDDCI and MVDD can be changed on individual 6600XTs (appreciate thats not really for this thread)
If you go higher, it will be higher, but I guess you can go as low as you want - it will still keep 650/1100 as mininimum - which is fine for hynix, but micron needs 1150 for my only card I have. So that really makes it much easier to overclock as 901 / 650 / 1100 / 950 are best and should always be used. Only thing need to change is VDD (take note, that if you make it too low it will bounce back to 850 or something) and once it is stable, change SOC values. I found that all cards work on 418 mhz and only need lower/higher vddmax.
Those micron settings for me of 630/650/1150 crash the GPU. The 930 and 950 are fine however. I use gminer.
Try 650 1200
very interest
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Guys, I’ve got 7 RX 6600, one MSI Z-490 Mobo, an intel 10th F processor, 8 gb RAM, 2 850 Modular gold psus and riser cards for every GPU. Can’t get it to work stable on HiveOS nor other SO. Its settings are what usually is here
After some random time, always one card goes off saying GPU DEAD
Hi @vicentinmateo, does your rig run ok without any OCs?
- if it crashes without OCs it might be another problem
(GPU dead usually means the OCs are a bit too aggressive and/or the voltages are a bit too low)
Can you post a pciture of your HiveOS screen?
Hey, thanks for replying. These are current screenshots
Right now a GPU went off but it doesn’t say anything related to gpu dead, or “hung”.
Now it said >GPU driver error, no temps in the notification list. Could it be a hardware issue? Will look for that this afternoon
[Edited with contributor comments - big thanks to niexasadas]
Hi @vicentinmateo, ok…based on info @niexasadas shared here recently you can try these “good starting point” OCs;
Please, please, please make a note of your current OCs and config before trying this. You may have to revert back to them at a later point.
1). Remove the Power Limit, its not needed for 6600s
2). Memory controller voltage is never lower than 650 even if you set it lower in the GUI
3). Memory voltage is never lower than 1100 (FOR HYNIX ONLY, use 1150 to 1200 for Micron) even if you set it lower in the GUI
4). Set your own fan speed or use Auto.
These OCs should work on the majority (90%?) of 6600s (anyone please post here if they don’t)
If these OCs work ok with no crashes for 24hrs+ then start reducing Core Voltage down from 700 to 690,680,670,660 etc until a GPU crashes then increase by +5 until the GPU stops crashing. Keep an eye on MH/s as you reduce Core Voltage, it will start to decrease as you get lower. Make a choice; Performance or Efficiency?
Lastly, you can reduce the SoC VDDmax from the default value of 850mv down to 800, 790, 780, etc until a GPU crashes, then up +5 until they stop crashing. Do this after you have stable settings for Core voltage. Again, this may affect MH/s so try to find the sweet spot that works for you.
Final note, if you are using the “starter” OCs shown in the pic above but GPUs are still crashing you can try this slightly higher setting for the SOC Frequency value;
(I only had to use this value of 534 on two of my seven 6600s, so try 418 first, it should work on most cards)
Useful commands = amd-info, amdcovc, amdmeminfo
If you want to know exactly what OCs were applied at boot = cat /var/log/amd-oc.log
[Note, I use TRM so I can’t comment on nbminer or any other specifically]
Hope this helps…however, I would first try to get your rig stable without any OCs just so you have less variables to deal with 
We are getting closer to the nirvana of a universal “out-of-the-box” set of OCs for 6600s
Any and all comments or edits are very welcome.
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Thanks a lot for your response. I will first try it with NO OC on it to make sure it’s not a hardware issue. Then, I will start applying these OC’s as you have mentioned. Thanks for your time and patience, in some days I will let you know how it came out
thx i already sent it back 
i tried on the big gpu slot …should have 3-4 … but whole board didnt start. maybe i picked a broken one
maybe i try another time some day
Hi guys,
I’ve been having this issue adjusting VDDC on my non-XTs. It was fine prior to updating to the latest HiveOS, but now I can’t seem to change the VDDC on them. I tried everything I could think of (even a clean install of the OS) beside re-flash the vBIOS, none work.
I can still adjust the core and mem clock though but not the VDDC. Also, what even weirder is somehow this only happens to the non-XTs while the XTs are just fine.
Please see the attached photos. New users can only embed one photo per post, so I’ll be continuing this in the next two posts.
The VDDC adjusted value of the non-XTs are circled in red.
Amd-info output. Green circles are what reflected my adjustment just fine. Red circles are what ignored my adjustment. Red and green underlines are card models.
TRM output. Red underlines are the VDDC of the non-XTs which I adjusted them at 620, but somehow it reads 768. Hence, I can’t get them down to ~45w like I used to 
Hi @csuttichujit, drop the Soc Frequency down from 1200 and VDD should reduce.
Alternatively, you may have set VDDC too low and it has ignored the GUI value and choosen a higher value to use. Try a slightly higer value than 620 like 625, 630, etc