Thanks for all the kind comments on my build. I really enjoyed building it and wanted somewhat of a showpiece in my living room.
I hand cut the top plate using regular old drill bits, hole bits, and a dremel cutting wheel. If you get up close there are some flaws in my cuts which is why I used a hammered look spray paint to cover up any imperfections. I had thought about drawing this up in CAD to have someone laser cut the plate. Of course that would look really good, but it didn't seem cost effective. Cutting by hand took me 3 days, but was well worth it.
The knob is Bob's stepped attenuator option. Since the RCA jacks were relocated to the rear of the cabinet, I used shielded microphone cable to protect the line input signal from unwanted EMI to get the attenuator in the front. Bob recommended the shield be grounded to the driver board and it worked magnificently; no noise, dead silent. I use a Audioengine B1 bluetooth receiver as my line in and play most of my music from the Tidal app. If you have not tried this yet, the premium subscription has HiFi and Master quality music which is quite good. This also allows me to change music and adjust volume from my phone or ipad while sitting on the sofa. The attenuator is almost not necessary using this bluetooth setup.
Voltage in Japan is 100VAC @ 50hz. I have not noticed any degradation with this voltage/freq.
I am using a set of Heresy III speakers and they sound amazing with this amp. However, my ears prefer a little more bottom end than these speakers produce and considering adding a subwoofer or two to the set up. Right now I a mulling over what sub and how to tap off the line input to connect them. At the moment I do not use a preamp but probably will build one sometime down the line.