SET amp comparable to First Watt SIT 1?

If the Volti model you are buying is the Vittora, you may be able to use a lower power SET amp using a 2A3 or 45, which opens the door to lots of options other than the 300B.  I have heard the Vittora at several of the Capital Audio Fest shows, and the very best sound in my opinion was with Greg Roberts' own 2A3 SET amps.  At one of the shows, when a room visitor asked Greg to play a particular CD he turned the volume up and said he would have to switch amps because he could hear some compression on peaks.  He then hooked up a borrowed pair of Border Patrol 300B amps with 18 watts.  For what it's worth, I didn't hear the compression with the 2A3 amps and this was a very loud volume, louder than I would normally find comfortable.  Also, to my ears the Vittoras did not have the same magical sound with the BP amps that they had with the 2A3 amps.  This wasn't just due to the BP amps being cold when I first heard them; Greg left the BP amps running for the remainder of the day so I had a chance to hear them after they were fully warmed up as well.  I am not saying this to put down the BP amps but rather to emphasize that for many listeners, such as myself, the 2A3 amps would have had plenty of power on the Vittoras.

That's right.  All amps sound different.  All tube types sound different.  Choosing a particular amp is very much a personal choice, and there are no absolutes here about one specific tube or topology being best.  One has to listen to a variety of different amps before making a final choice.  In my case, if I had bought the Vittoras and I came close to doing so, I would have used my 46 SE amps which have even less power than the 2A3.  I am pretty sure the 46 amps would have sounded great and would have had more than enough power for my needs, but I suppose I will never know that for certain.