I built the Audio Note Kit 4.1 LE and subbed in some VH Audio CuTf caps on the output, plus rolled all of the tubes a fair bit. It is a great DAC for the money IME, and it easily displaced my EAR Acute with greater body and "feel" of all instruments, more completely realized timbre, and a greater 3D soundstage. I still use this DAC in my second system.
In my principal system I use a Lampizator Golden Gate, and it is just so much better than the AN piece - - "shake your head real" many times. The Lampi gear has all of the strengths of the AN, just more so. The Lampi Big 7 I used before this was also clearly superior to the AN in my system (and it teased me into reaching for the GG). It might be worth your while giving the latest Lampi product a spin.
Interesting. I had a maxed out DAC 4.1 Kit as well and it was great. The DAC 5 Special is better of course. I am still in the process of replacing the tubes and swopping out the copper caps, so will get an idea of how much better in a few weeks, and report back.
Yes, I do find the Lampizator Golden Gate interesting. I had an option to buy a GG recently but it was the earlier unit without the discrete PCM board which upgraded the Redbook. I haven't heard one yet, and read it is very good on up sampled PCM to DSD.