what OS, is your video card overclocked?  If so what are the settings?  How many watts is your power supply?  How much wattage you showing at the wall?

Did you look at your system logs to see if any errors were reported?

If you are running Windows, do you have the latest Win 10 Creators Edition or? 

You didn't give us much info to go on... 

yeah you'll lose a lot at 60 TDP if you move to zcash.  I'd stick with ETH as I'm running three 1070s at 85 TDP on Equihash and I have 510 watts at the wall.

sounds like you are using Windows.  If you are, download GPU-Z then open the program.  On the Sensors Tab looks towards the bottom and you will see an entry named:  PerfCap Reason.  In the next column it will list the reason, for me it's power as I'm only at 85% TDP.  But when I raise my percentage higher than other reasons show.  I'd use GPU-Z to compare the card with the slower hash to the values of the normal cards and see if it will give you a hint to the issue.

Nicehash has a lot of fees.  Do better mining on your own. 

use the Nicehash profitability calculator and set it for your 980:  https://www.nicehash.com/?p=calc

--this will give you your cards hash rates for various algos.

Then go to http://whattomine.com/ and in the lower right, pick the 1060 or some nvidia card, put 1 in the box and make sure the button turns green.  Then at the top click on whatever algos the Nicehash calculator said your card did.  Put in the actual hash rates and then you'll see the most profitable coin.

Depending on your coin, you will probably do the best with Claymore, EBWF, or ccminer.  I've found the easiest thing to do until you understand the various algos is to go to a mining pool and click on the Getting Started or Help link and they will list the various miners and give you the info for their pool.

you can do miner --help and it will show the options.

add this to your miner line:

--templimit 85

You don't mention what OS you are using.  I have 3 1070s undervoltaged to 85% TDP and am pulling 512 watts at the wall using a Kilowatt meter.  You don't specify if you are undervolting or not.  At least with my current settings there is no way I could run 6 GPUs on a 1000 watt P/S.

With 5 GPUs in, check the power draw at the wall and see how close you are to 1000 watts.  If you don't have enough power you can either go to a larger single power supply (1300 watt) or get two 750 watt and get the connector that turns them both on at the same time.

Also you don't mention what happens when you put the 6th GPU in, does the system not boot or does the system turn off when you start the miner?

I believe ethOS has a help forum.  You don't mention any specs and you don't say what the error is on the next screen.  I'd install Ubuntu and the AMD drivers and see how it does. 

If you know your hash rates, I recommend going to this site and entering your number of video cards and see what is the most profitable. 

http://whattomine.com/

it will also tell you how many days for ROI, but I don't know if it "knows" when the difficulty increases. 

Also you need to consider if you are mining and holding vs mining and selling/shapeshifting...

http://whattomine.com/

on the lower right, click on the button that says 1070 (should go green) then put how many 1070's you have.  Then you can calculate and see what is the best coin.  A lot of options available...

I fired up the windows miner on my Win 10 Celeron 3900 rig 8 GB of ram with 3 * 1070s and set the virtual memory to min 28 gb to max of 30 gb.  CPU was max'd at 99.0% and would blue screen after about 3 mins.

EBWF mining ZEC puts the CPU at about 20%.  My results confirm what reb0rn21 was seeing.

Looks like I'll have to dual boot Ubuntu to mine this coin...

So any word on this coin or any windows miner?  I was running Linux at a time, but went to Windozes to OC and do system tweaks--NVidia fought me in Ubuntu.  I can always make the rig a dual boot and run the Linux miner, but I don't see anyone on the Suprnova mining pool. 

Anyone have a current state of this coin?  Thanks!

I would recommend a wired solution, wireless can cause quite a few issues.  As far as the AC perhaps you can work out the amount of heat a card generates and work it back to what AC solution you would need.  Luckily I have a basement in my rental house...if only I had 220v but the landlord would freak   

https://whattomine.com/

this site will let you choose what type of GPU you have (AMD/Nvidia) and gives you a avg hash rate for your setup.  You can add your power costs, pool fees and hardware costs to see how much you will make. 

I've been mining Zcash with my 3 x 1070 rig.  Are most ppl holding onto ETH or doing a shapeshift to Bitcoin or another alt?  Trying to figure out the best strategy. Thanks!