Ps Audio BHK preamp Vs ARC best preamps

Well if you like the idea of the BHK preamp, BHK himself (the man, not the preamp) extolls the Aesthetix line stages as just superb. I have one and I can also assert that they are simply awesome...all tube, maybe every so slightly more liquid and tube-like than ARC products.  Extremely well designed, great construction. 

If you're looking to add tube warmth that can be adjusted then you will get more with the BHK with NOS 12AU7 or even 6DJ8 tubes than you will get from the ARC with it's Sovtek/EH 6H30 tubes.  The non-Reference models may still give you rolling options but ARC preamps are not known for typical "tube warmth."  

Has anyone compared them to something like the McIntosh C2600?

From what I've heard, the through-the-preamp or direct-to-amp question is like many in audio:  both can be good, depending on the usual factors.  Impressions I've gotten indicate audiophiles are split about 50-50 on the question, both, no doubt, with good reason.  Meaning, aside from any meaningful technical questions such as that as raised by JohnnyR above, the only real route is to try both.  My preamp maker and dealer feel, for my equipment, it's better through the preamp, although "no one understands why".
Jim Heckman