The current lineup of Headroom Modules in their higher end amps (Desktop, Home, MAX) all use a Jung-designed discrete diamond buffer on the output. As far as solid state devises go this circuit is well suited to your Grados in its ability to provide plenty of current which is what the low-ohm Grados crave. And based on what I've heard of Headroom's lineup I bet any one of them would pair quite nicely with Grado cans. If I were you I'd shoot for an amp with at least the Home module in it.
Finally, as far as the whole Grado/tube synergy is concerned I've heard my modified HF-1s out of a good deal of both SS and tube amps and my favorite was a SS amp.
__________________
SB3/Arcam CD73 -> Hertsens Signature DAC -> Project Menace -> HD650 | Woody HF-1
-Head-Fi Feedback-
d-_-b
|