First Watt F8, passive preamp, DAC

As another data point, I ran my Pass Labs DAC (about 1.8V max output unbalanced) into my SIT-2 (18db gain) into 94db efficent speakers with no gain issues whatsoever.  

As I type I am running the same DAC with the volume at about 1:00 (so roughly 1.0V output?) into my preamp at 14db gain into the SIT-3 with 11.5 db of gain.  1V output with 25.5db of gain is plenty on my 94db speakers.  I typically listen around 83-84db average, so pretty loud.

I think you should be ok with digital, do you know the output of your DAC?

I have run a DAC directly into a SIT-2 which is 18db of gain and it worked great.  Running the same DAC into a SIT-3 with only 11.5 of gain was also fine, although I did run out of headroom on some CDs with really low peak levels.  But even inserting my Pass X2.5 preamp with only 4 db of gain fixed that minor issue.

The J2 would be a better option because it has balanced inputs, and if you run balanced interconnects from your DS DAC you will double the output voltage to 2.8V.