Quick update: I received a handful of replacement parts and the proper standoff from Bottlehead yesterday. Amazingly fast shipment, thanks very much to the parts collection and shipping crew. I replaced both transistors on the "A" side of the C4S board, but the LEDs still did not light. I then replaced the two "A" side LEDs (glad I requested them) and everything lit up properly. I went through all resistance and voltage checks and everything was right on the money. Whew. Plugged in my headphones and it sounds fantastic. I only had about 30 minutes to listen before needing to hit the sack, but I think the "boxed in" sound I had described previously is pretty much gone. Whether that is a result of burn-in, the C4S installation, some combination, or something else completely is an open question, but in any case this thing sounds great. I left it looping music all night to continue the burn-in process and am quite looking forward to a lot more listening sessions. I've also received a few more 6dN7 tubes (man those things are inexpensive) so I can swap them around and see if any seem particularly well matched. Thanks everyone for the feedback and especially to Bottlehead for quickly getting me the bits and pieces needed to rectify my problem.
-John
