Upgrade Harman Kardon AVR 335

Currently using the HK AVR 335 in my system. I use the preamp outputs for the front R/L to feed a tube amp and my Magnepan MMGs. I also have a seperate DAC and I defeat the tone controls to get as clean as possible. I'm thinking about getting a separate processor and a couple of amps, but mainly to improve my two channel sound. Due to my constrained budget, I'm considering a B&K Reference 20 or 30, or maybe a Lexicon DC-2. Lexicon and HK share some technology, so I wonder if this will make much of a difference, especially since the HK actually uses newer chips. Also, it's my understanding that the Lexicon converts analog to digital anyways. Does anyone know if the HK does as well?

Would the B&K be a better choice if my main goal is to improve two channel playback. I'm actually quite happy with the HK as far as 5.1 is concerned.