I can help with a few of these based on my own testing...
1. Liner - I’m using intuitions. After forming them and the boots I’ve had no issues with heel hold or all day comfort. Toes get kinda cold towards the end of a session, but nothing worse than any other boot I’ve had.
2. strap - the Velcro strap is ok. I swapped mine out for a booster just to make it easier to tighten down.
3. For soft boot angles, I’m close to max forward lean. With the green springs, the boots are more responsive than my Salomon malamutes on toesides and are comparable to any stiff bindings on heel sides. You should have no problems driving the Fish.
Hardboot angles (>50 degrees) are where I’ve been running into a challenge. Even with the rear boot lean max’ed out, I still can’t get into the right crouch position. I need some heel/toe lift, so that’s where I’m stuck for the moment. The boots were stiff enough to drive an alpine board at ~45 degree angles, but I had a lot of overhang and so couldn’t really push it.
4. I’ve used this with both a Dupraz and an Osin 3800, the boots worked brilliantly as a soft boot replacement on both powder and groom. I end up with less overhang as well, which is a nice bonus.
Really curious if you’re able to get your position worked out on the Madd, and how the boots feel for you at those angles.
Good luck!