Oh yeah, If it's anything like the F1J it's good in the winter and very bad in the summer. The thing gets "HOT" but that's what you "SHOULD" get with a pure class A amp. If they didn't get hot - I would be worried.
Add a pre amp for more gain or for less gain? The F3 is a SE amp correct? That's odd, the pre amp in the AMR is "Killer"...
Can the Stratus keep up with the HE-6?
Imo the HE-6 sound pretty good with the Stratus. When I tried the Krell KAV- 400xi integrated it lacked the soundstaging and realism of the Stratus (I really wanted to like the Krell because of its simplicity). Same for the F3 with the Krell as a preamp, nice bass and treble but lifeless.
As for the heat, it's a killer in the summer (one of the reasons I sold my EC Zana Deux).
I have no doubt the preamp in the AMR is good, it just doesn't have enough gain with the F3. I tried it with my McCormack Deluxe Edition Power Drive DNA-2 which is an 82 Lbs 300 Watts into 8 Ohms beast, sounds great but again the heat and power consumption (seems over kill for hp listening).