What Preamp should I use

If you enjoy the clarity of the Adcom GFP-1, you are in for a real treat on the later generations of budget preamps. I would not recommend the GFP-555 in any version. Adcom made some fairly decent amps and tuners (which I used in the 80s and 90s) at the time of this preamp, but there were so many budget models from PS Audio, Mccormack and Superphon to name a few that were far more open and resolving than the Adcom GFP-555. I have not hear the newer Adcom preamps but the 7xx models get a lot of praise so check them out as well.
John

You should let us know your budget. Maybe you could try a used tube preamp? You could always get an Adcom GFP 555II for cheap and it's much better than the gfp1.