Preamp

The Ref 5se is definitely better than the C2500.  Although I did not compare directly with that particular unit but instead, the comparison was made with the Mcintosh C1100 dual box preamp running through my Pass Labs 160.5 monos and the Ref 5se was still more musical and better in all parameters.  My dealer was informed me that the Mcintosh has a lot more problems with their preamplifiers over the years than Audio Research and my researches over the net had shown that to be true.  Good luck on your preamp searches.

Would recommend the Reference 5se which is definitely quite a step up in performance than both the GSpre (take a look at the interior of both units and you will see the Ref 5se has much more capacitors and beefier power supply) and the Mcintosh C2500.   If you could afford, go for the Reference 6 which is on a whole new level of performance...fast and palpable, even more transparency, more 3D holographic imaging, more deep tight controlled bass.  I would not imagine any other tube preamp under $20K could even compare to the Ref 6.  Especially when running with the Pass Labs amp, the Audio Research will be a match of heaven!