Joe, I've listened to the C2300 vs. the C50. I think the biggest difference between the C2300 and the C2500 is the built in DAC on the C2500. Also, when I auditioned them the C50 wasn't capable of playing 24/192 files. Both preamps were connected to MC601's and the source was an MCD500.
The C2300 had that nice tube sound. Rich, full sounding music that is associated with tubes. Very nice airy highs and good bass along with a sweet midrange. The MC601's delivered the speed and punch and the C2300 gave the music life. The C50 didn't quite have the openness but the bass was definitely tighter and more impactful. Surprisingly, the two didn't sound that much different.
I went into this thinking that I would easily pick the C2300 over the C50, being a tube guy, but after listening to both of them I wasn't so sure. I really liked the C50 and everything it brought to the table in terms of connectivity and useful functions. I really like the looks of the C50 with the EQ knobs on the front of the unit. If I remember correctly the C2300 has EQ functionality as well but you need access the remote to get to them. I wish I could have heard the C50 with tube amps. I think that would be a good combo. Like I said earlier the C50 didn't have the ability to play hi-res files but I believe that is fixed now. I also see that the C2500 has a built in DAC which brings the two units even closer to one another.
I almost hate to say it, but if I was buying one of these today I would go with the C50.