You sent me a pm about this, but I think I'll just respond to you here. I'm not the most knowledgeable about amplifier circuits and whatnot, other than what I read here.
If you're looking for circuit diagrams and information about the Elekit amplifiers, Victor (vkung here on head-fi) is the primary person distributing the Elekit amplifier kits here in North America and should be able to help you out.
There are a couple of things you can do to modify the TU-882.
Upgrading the coupling capacitors. http://www.head-fi.org/t/516864/tu-882-vcap-upgrade
I didn't spring for the V-caps (pretty pricy), but did purchase some decent Mundorf silver-oil capacitors (still pricy, but not as much as V-caps) to replace the four coupling capacitors. I found it a worthwhile upgrade, cleaner mid-bass and treble.
Rolling tubes. I have some NOS United 2C51 tubes in mine because I found a pair for a fair price. Only minor improvements over the GE 5670 tubes that come stock with the amplifier. If you can find WE396A tubes, those should be a nicer upgrade, but again, very pricy due to scarcity.
Swapping the potentiometer. Some people find the stock pot in the kit to have a little too much gain, so low impedance headphones, even on the low gain settings, get too loud too fast. I do use UE's airplane adapter to add a little impedance to my IEM's whenever I plug them into the TU-882 so that they are more usable.
