Hi, first of all, regarding the Sonica vs UDP, I know that the processor chip in the 205 has a greater capacity. I am not sure which chip it uses for DSP, etc.
Regarding mods for the 205, the mod that we offer for this unit is already significantly better than the 105 mods. The tube circuit has been completely redesigned and offers a lower noise floor, better resolution and deeper and more defined bass. It IS our flagship mod to date and so you can really understand how heartbreaking it is to us that Oppo decided to stop making the UDP-205 and all other products.
We do offer the Audio Magic Pulse gen as an additional mod option. The bybee rails cannot be installed because of the way the the DACs Vref circuit is now implemented, all surface mount. To their credit however, they also improved this power circuit significantly also.
The UDP-205 is the best player that Oppo has ever produced and our mod is the best mod that we have produced to date!