Aragon 28K - what changed with the Mk II

I'm sorry this is not a direct answer to your question, but I have a 2004 amp, a 4004 amp and a 2004 MKII amp, the MKII sounds better. The big deal at the time was the MKII's used higher grade and better matched Toshiba transistors. Those transistors, as I understand are no longer in production, highly desired and sold counterfeit on ebay. Back in the day, Aragon offered to upgrade your original amp to a MKII for a very nominal fee, maybe $200. You got the new transistors and a "MKII" paper sticker on the back of the amp. Both were Mondial, before Klipsch.
I bought my daughter a 24k or 28K, which I believe was also MKII and the big deal there was the upgraded and more reliable external power supply in the triangular case and the Penn and Giles potentiometer. Again, Mondial designs just before Klipsch bought the inventory and became the distributor. Shortly after Klipsch bought the name, the product changed, most notably the look.

Ebay has a short online history about Aragon.

I'm pretty sure my daughter's preamp is pre Klipsch. I bought it from a former Aragon employee after they went to Klipsch who "happened" to have a few around after he left. I'm willing to bet that it's a Mondial product too, 'cause I would have remembered otherwise. It's built like a military piece, is black and matches my other equipment. That guy made me a deal I couldn't refuse for a new Aragon Preamp. My daughter loves it.