Tube amp Low end Bass question

+1 on duals subs!

Those Omen's will sound amazing with a tube amp.  You need 15w to 18w to drive them well with plenty of headroom to hit 105dB for music.  

The MC275 is a lovely amp but you will find a SET will sound heavenly in comparison and your speakers are more than efficient enough to be driven by a SET in any normal size room.  

Two subs are not essential but it will improve balance.  Key is getting the crossover point and placements just right.  I have a SET amp and two 10" subs paired with standmount speakers.

I've been using 2 RELs for years with a few different main amps (current amp is a Dennis Had single ended little gem) and they're fabulous. Bought both RELs "used but mint condition" for relatively little money and can't imagine not having 'em. Klipsch Heresy IIIs with a REL Q150e (10") and Q108MKII (8"). 

I really like to crank it sometimes, I am a little hesitant that 15-20 tube watts may not be enough with the ZU's. My current SS amp is 80 watts and it does not peter out and feels there's plenty left. That is why I was thinking the 75 watt 275 may be the trick. 

Is the Quicksilver 60 Watt Monos SET?