wow , what a great search engine. I get an email that someone has (mistakenly) commented to a thread I was part of over 4 years ago! I don't do as much with HeadFi as I should, but I'll do a brief follow-up after looking over all I wrote years ago.
Even though much of the rest of my system has changed, the SFI Line1 has remained, though now much improved -- BB volume control chips, the perfect tube combination, new AC power cord and conditioning, hifi tuning fuse, a full SE factory upgrade of all signal path passive components to the best available, pearl tube coolers, various vibration damping and isolation, etc. And I just recently picked up a 2003 stepped -attenuator Headroom Max now being upgraded with their 2007 Max modules and HEXFRED power supply diodes.
But the Max -- even with its 2003 reference modules -- definitely had the upper hand over the greatly-upgraded Line1 with headphones. Subtle improvements, but consistent. Remember the Line1 headphone amp board is unchanged from its 1997 design, but it's getting a cleaner input signal from the upgraded preamp section. Comparing the Max and Line1 as preamps was more surprising: they sounded damn-near-identical, surprising for any 2 preamps, much less the totally differing design approaches between these two. When I get my Max back next week, it might even sound better
So with all the headphone amps that are available now vs 2002, buying the Line 1/2/3 for headphone duty only would be a monumental waste of space, money and electricity. I still think it remains one of the best designed and flexible preamps out there anywhere near its used price. I often DO listen to headphones with it when I want a more relaxed less clinically revealing music experience than the best headphone amps -- it certainly doesn't suck, but probably any HP amp over $500 will sound better...