Is the Adcom GFP-750 really that good ?

I would tend to agree with Plato and Daltonlanny on the sound of the 750. I had a $200 passive Creek OBH-12 that was awesome sounding! It even had a remote. I would have kept it except there were only two inputs. I liked it so much I thought passives were the way to go, so I picked up the Adcom. It was disappointing in my system. Sounded much like the two above discribed. The Odyssey Tempest is outstanding and took my system to the next level.

I agree with other respondants who opine that the GFP-750 is an exceptional value when purchased used. I recently replaced my GFP-750 with the new "Gain Cell" preamp from PS Audio. The new preamp is still breaking in, so I reserve final judgement, but I can confidently state that it is more resolving than the GFP-750. First impressions include a lower noise floor and higher resolution of detail, as well as greater dynamic contrast and speed, the latter particularly noticable in the bass region.
The only amplifier that I have paired with either preamp is the PS Audio HCA-2. The GFP-750 works very well with the HCA-2 in passive mode, using either single ended or balanced interconnects. Resolution is exceptional and dynamics are surprisingly good. Avoid SE cables, however, if you intend to use the GFP-750 in active mode with a very transparent amp like the HCA-2. With SE cables in active mode I consistently found the sound to be veiled, and fatiguing with extended listening, in comparison to the passive mode. Upgrade to a good set of balanced cables, however, and the active mode sounds just as transparent and sweet as the passive mode, with a touch more heft in the bass region. I enthusiastically recommend Synergistic Research Kalaidoscope Phase II cables (balanced) as an excellent choice for anyone interested in pairing the Adcom GFP-750 preamp with a PS Audio HCA-2 amplifier.

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.

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

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.