Hi, thanks for your interest in the H90. To answer your questions:
1. A Program change sent to the H90 will load a new Program, which is a combination of 2 Algorithm Presets. You cannot send a PC that will only change one of these Presets, it will always load a new Program. You would need to make your Programs before hand to have the desired Presets, and then load them via PC messages. You can use the pedal UI or H90 Control to load a new Preset quickly and easily, but this cannot be done remotely.
2. I just tested this with Ableton by sending a PC followed by 3 CC’s mapped to 3 different parameters and the H90 handled this just fine.
3. Yes, TremoloPan has the option of using a Ramp for the mod source. You could probably accomplish this with some other Algorithms too, Undulator is great with a Ramp mod.
4. These may fit, but I can’t confirm this. I don’t have any of these to test the size, and the measurements look like it would be a tight fit for a stereo pair. We like the Squareplug SPS4 connecters.
Let me know if there are any other questions I can help with.