The Q701 loves warm-ish SS amps, IMHO.
However, don't let that keep you from the Modi+Magni. That combo is worth it, it just may not be the most ideal for the Q701. Overall, the M+M is a better combo than the E17+E9K SQ-wise. The E17+E9 has more versatility though, with multiple inputs, including optical.
As for SS amp differences, they are subtle. Don't expect a highly noticeable change. If I could make up numbers, I'd say something along the lines of it being the last 2% difference in a headphone's innate sound. As long as a headphone has enough power to funcytion at it's optimal level, differences won't be big, and sometimes unnoticeable.
Edited by Mad Lust Envy - 12/17/13 at 8:52am