I own the Max and the PreHead (AD8610 version), and both are fantastic. Cost no object, I'd personally recommend the Max over the PreHead (which is the big brother of HA-2). I prefer its crossfeed to the PreHead's; I think there's a more organic image fullness with the Max, too (crossfeed on or off). When, for example, I'm listening to orchestral music or live jazz recordings, I find the Max gets me a bit closer to the feeling of a live experience.
I think the PreHead is a stellar value, though, and maybe one of the best audio values I've come across. It is not priced like a cost-no-object piece, but it performs very much like one. It's good enough that the Max and PreHead regularly swap places in my home and office rigs to give me the different flavors of each, which isn't something I would've expected from something this affordable. What doesn't it do that the Max does do for me? It ain't missin' much, but its sonic refinement is, overall, just shy of the Max's. If I had to choose only one (yeah, right -- they're both staying), again, the Max would get my nod if you can front the price of Max admission. NOTE: I prefer the Max with the Sennheiser HD-600, Grado HP-1, Beyer DT-931, and Etymotic ER-4S. The PreHead sounds better than the Max when it comes to driving the AKG K-340, though.
On the crossfeed specifically, I like the greater tonal neutrality of Meier's crossfeed more; but I like the HeadRoom crossfeed's spatial qualities more -- I feel that HeadRoom's crossfeed better maintains the integrity of the space. A crossfeed with the HeadRoom's headstage qualities and the Meier's tonal qualities would be, to me, just about the perfect crossfeed.
A little off-topic, the TwinHead MK II will be on my desk next week, so I'm definitely looking forward to seeing (well, hearing) how two of the very best solid state headphone amps compare to what's anticipated to maybe be one of the best tube headphone amps out there. Considering Antique Sound Labs' later products appear to be reaching greater levels of refinement, this should be a good time. By the way, did anyone else notice that Harry Pearon of The Absolute Sound, in the latest issue, rated ASL's Hurricane monoblocks as the best amps (speaker-driving, not headphone) he's ever heard? I hope the TwinHead MK II has some of the Hurricane's apparent magic.
EDIT: As though this post didn't stray enough from the original post....I just noticed that he was asking about the old Max. Sorry 'bout that, man.