I had a modified 777ES, with Kern mods on the transport board, Superclock 2 and high quality resistors and a Jerry Ozment designed tubed/transformer coupled output stage (essentially the analog section of my Audio Logic DAC). The sound was, to my ears, better than most units I have heard from dCS, Esoteric, Accuphase and even the first version of the EMM Labs gear. I replaced it with the EMM Labs CDSD/DCC2SE combination. I lost a little warmth in the midbass region (which also muddied things up just a little there) and gained a little better resolution, dynamics and deep bass reproduction. My friend who bought my 777ES loves the sound of it, he has actually cut back a lot on his analog listening because of it.
You will not get your money back from any mods, and repair work on one may be a little hard to get (I believe many of the modifiers can do repairs, though), but sonically a well-modified unit is more than competitive with what's out there in today's marketplace.