I'd be curious to know how many here have a speaker rig - even a modest speaker rig. For some bizarre reason, many Head-Fiers seem to lump the Audeze cans and the HE-500 in with the HE-6, automatically assuming you need a 6-Watt headphone amp to drive them. FWIR, that simply isn't the case, but as Justin pointed out the GS-1 will function as a pre-amp : those wanting to run big orthos can use the speaker posts on their integrated/power amp.
Dont like the reviews of the GS-1/GS-X neutral sound sig ? Benchmark, CEntrance, Peachtree, RSA and others all make variations on the 'Swiss Army Knife with a pre-amp' theme - whether any of these are going to give you the aforementioned transparency and flexibility of one of Justin's home amps is a question only you can answer. In any case, I dont get this obsession with finding a single headphone amp that drivee everything from high-sensitivity, low impedance IEMs to the HE-6 equally well (!) for under 1K when you can be killing two birds with one stone - driving speakers and orthos from a speaker amp. I was initially skeptical when I read that folk were happy with that setup, but there are numerous Head-Fiers who claim to enjoy their 'big' HiFiMan cans from a speaker amp - given the low cost of that option over a 6W headphone amp, I cant see how you can go wrong. Spend the money you save on better sources.
Of course, those with money to burn will always dash out and buy the biggest and best, but the OP seems to be looking for midrange budget solution that wont involve days/weeks of tube-rolling. I understand the Head-Fi fascination with 'moar power !'', but there are times when it just gets silly for those of us who don't have a trust fund. The GS-1 remains on the shortlist I have had for the last 2 years, but buying the amp before I get a decent source is just a waste of time and money. Even if it means holding off for another 2 years, I suspect that Justin will still be making and selling amps - they certainly dont seem to appear in the FS forum too often.