I would also recommend upgrading the amp to the Odyssey amp of your choice and go with the best one you can afford.
Recently I auditioned my NAD C372 against another much larger amp and preamp combo (not an Odyssey, but another well-respected manufacturer that offers a 20 year warranty). Switching between the two amps and using the NAD as a preamp made a large improvement in the clarity of the midrange and deepness of the bass. Switching preamps made some slight improvements, but to my ears the most significant improvements came from changing out the amplifiers.
Also buying a used preamp is a very safe bet. They contain no moving parts and do not generate a lot of heat. Hence, their lifetime should be many years of trouble-free service.
Just noting my observation.
Good luck,
John