The ES2 sounds GREAT with the "M"-mod Hornet -- the best of any portable I've tried so far. I haven't been able to get hold of a current Xin amp, yet -- and will try with PRII soon. The Portaphile PV2^2-LT1210 Maxxed has great HF extension, detail and nuance and great imaging -- but has a pronounced hiss with the ES2; the AE-1 has even more hiss.
The original stock Hornet (with Nichicon capacitor) was too bassy/warm and too soft in the highs for the ES2.
The current "M" Hornet is wonderful, with a soundstage (illusion of course) that extends well beyond the ears with good recordings, has good dimension/spatiality and imaging, rich mids, and good HF extension and detail without being fatiguing.
I haven't yet tried it with any impedance adaptor or attenuator (to extend the volume control latitude). I play the Hornet between 1.5 and 2 on the volume pot "dial".
Be warned that the "M" Hornet takes even a little more "burn in" time than the original did. 350 hours seemed to be enough, but it continued to improve after that, and the bass energy became more manifest around 400 hours (rough guess since I had stopped noting playtime by then).