Is the Adcom GFP-750 really that good ?

Try a used Parasound P/LD-2000 -- I had the Adcom and like the P/LD-2000 better. It seems to have more body, and is a bit more musical (while retaining detail). By comparison the Adcom sounds dry and thin. Others who I've spoken to who have tried both say the same thing. I think the Adcom is a very good unit for the money, but I also feel it's somewhat overrated.

I bought the Adcom used on Audiogon. Made a big difference
in my system. It's worth the money. I love it.

Q: Is the Adcom GFP-750 really that good ?
A: Yes, and it's an exceptional value when purchased used.

You may also want to consider Marsh P2000, the Rotel RC1090, and the Quicksilver Remote Control Linestage. All of these preamps retail (new) for $1200 - $1400, and all are included in TAS's "Recommended Products" list. The Marsh P2000 is also designated as a "Editor's Best Buy". However, IMO, none of these preamps offer any overall improvements in sound quality compared to the Adcom.

I have owned both [several times].
The Parasound P/LD-2000 is overall sonically superior to the Adcom GFP-750.
I own a pair of Parasound Halo JC-1 monoblock amps, and the P/LD-2000 matches up extremely well with them.
Don't get me wrong, the Adcom is a great preamp. It is a bargain for what it does, especially used.
It is very transparent, dynamic, and detailed, and has excellent bass.
But: As Plato said, it is alittle dry and thin, has a somewhat recessed lower midrange, alittle etched and grainy on top, lacks ultimate top-end air and decay, and is somewhat dark sounding on vocals, especially in the Active Mode. It sounds sort of "HI-FI", if you catch my drift! It is alittle better in Passive Mode, but still has the same basic sonic signature. It is probably a good Class B preamp if it were rated similar to Stereophiles rankings. I do not feel that it is a Class A preamp. It does match up extremely well with the Adcom GFA-5802 power amp. Great as a matter of fact!
The Parasound P/LD-2000 is an underrated preamp! I love mine.
It is extremely detailed, extended at both frequency extremes, full-bodied, spacious, and gives true palpability to vocals and instruments.
I used to also own a Pass Labs X-2.5 and a Pass X-1, which I liked very much, but, in the end, I keep going back to the P/LD-2000. It has a certain musical "rightness" that the others lack in my system.
Results may vary in other systems and with musical tastes and priorities that differ from mine.
To each his own.