I'm a lowly HO. I'm having an AS system almost (smaller sizing) like this installed next week. I have an existing Aprilaire 760 humidifier that I'm hoping to use, but I'm wondering how well it (and your choice) will perform on a heat pump.
I came across a new steam unit that Honeywell just came out with called TrueSTEAM. And it connects perfectly to an IAQ as far as I can tell. There are a few threads on this board about it.
BTW, your systems sounds great to me. But them again, I'm just a lowly HO.