I just joined up today so here's my 2 cents worth re: Walter ( hope that's not price gouging ! )

I purchased a bunch of stuff from him that was backed by great service each time. KC II speakers, DSpeaker DAC, 2- Emerald Physics EP100.2SE Amps & Project Tube Box S
phono pre-amp.
Here's a couple examples that speaks to his character & customer service.
1) I was having a difficult time connecting the two mono amps to the speakers. I called Walter and he
sounded horrible over the phone. He told me he was running a 102 degree fever but still walked me through the installation.
2) The other occasion I broke off the tiny little plastic dip switch to my phono pre-amp- Geez, why do they make 'em so delicate ? Anyway, I called Walter & he contacted the distributor that same day. 2 days later, I had a new replacement !
I haven't dealt with any purchased mods from Underwood but, Walter recommended I try out the beeswax fuses for his amplifiers. The improvements were moderate- I gained about 20% more width to the soundstage and I can crank the volume to resemble a Who concert in my listening lair with excellent clarity.
He's a good guy for the industry.