Mcintosh

@g_nakamoto:  The MC602 commenced production ~2000 and is still available, while the MC2600 ran from 1990 to 1995.  MC602 is quad balanced, was tested to a far wider frequency response range and has a better S/N number. 

MC2600 has better specifications than the MC2500, but both are very similar.  Note that they are fan-cooled, while the MC602 is convection cooled.  Additional details on both can be had from Roger Russell's site here:  http://www.roger-russell.com/amplif2.htm.  

I have one 2500 and was thinking of getting another. Then came across a 2600. On another note what are some thoughts of either of these vs the Theta Citidel mono blocks?

effischer, i see that the 2500 and the 2600 are enclosed. i guess that's why they both have a fan. the 602 is open.

@2channeljunkie I can't offer any input on the Theta amps; never ran across any.  I vastly preferred the MC2500 to SAE and Phase Linear at the time, but found the Threshold Stasis to be a bit more enjoyable with the turntable rig I was using (Magnepan arm, DV23 Ruby, Sota Sapphire).  Couldn't afford either, so stuck with my Hafler DH220 until I could swing my Belles Model One.  

@g_nakamoto Not necessarily; the 2500/2600 were designed as caged, rack-mount units and McIntosh decided to produce a form that could be used both by consumers and professionals.  That's why the fans are speed selectable and can be set to thermostatic control.  602 is strictly a consumer design; glass faceplates don't travel well in Anvil cases.

Grateful Dead use MC 2300