I couldn't help myself. I made some A/B comparisons this morning. It is not really a fair comparisons yet as the new Folsum design has a lot of burn in ahead of it and it may come around a LOT. Again, the amps use the same chips.
As mono-blocks my amps have shorter speaker cables. They are just alike, but shorter, and I have always preferred them a little over the longer ones. The shorter ones also do not touch the floor either.
Also, my amps have no coupling caps at all. There is really nothing better than having no cap in the path. However, if I use either of my two outputs on my pre-amp that have a full range output then my amps won't come on. It leaves too much DC offset (I think) The coupling cap in the output of my pre-amp, that is a 3.3uF Jupiter cap, is just too big. But the third output on my pre-amp has a much smaller Sonicap Platinum and the amps work just fine with that output. So switching between the two amps means moving to a different output on the pre-amp too.
I would also mention that the input sensitivity is very different between the two amps. The Folsum model has a much higher input sensitivity level, and I do like that. But it also means that with A/B comparisons to my amps that I have to adjust the level on the servo subs with each switch.
The Folsum amp may have a little more output, drive, and dynamics, due to the higher voltage levels applied to the chip, but it was hard to tell much difference in that regard.
The Folsum amp also has a little larger coupling cap and plays a little lower than my amps. It works the lower woofers in the NX-Otica a little more and adds a little more body. I like that too.
The lower vocal region on the amps are really close. There is a little more body to the Folsum amp but not much. Upper vocals are softer for sure. It sounds a lot more like my tube amps in some ways than my chip amps. They are super musical and I could listen to them all day long.
However, at this point in the comparison (not much burn in time on them) they really give up upper level detail to my amps. My amps are sharper and sound a little more like a solid state amp. Air and space around everything is more present with mine. The Folsum amp is a lot more two dimensional verses mine. Mine present a deeper more layered sound stage. Some more time might change things in this regard a bit and I bet that it will.
I will say this though. If you aren't using one of the Folsum amps then you need to try one out. I think they are really tough to beat no matter how much money you spend. Granted you need reasonably efficient speakers, or you do not need high SPL levels. With the NX-Otica's (about 93.5db sensitivity) they may be all the power you ever want or need. For what the kit costs are it's a no brainer. They don't require a lot of parts either so spend your money on good quality wire, connectors, etc. It makes a difference.
I am looking forward to hearing what they do after more time, but so far a huge thumbs up from me.