Please could you describe a difference between them? Between Phoenix and dragon in SQ. I just ordered a Dragon amp and thinking about phoenix.
Sorry, been on travel, Dragon is better in my opinion, its more spacious, you can tell immediatelly you have something "special" when you try it first time, phoenix is more laid back but also very nice, its more a matter of taste I guess. Both will give plenty of detail, full spacious sound, great separation and rich bass. With those cards unfortnately gain setting makes no difference. If you ordered dragon - enjoy, good choice, no need to get phoenix, dragon card makes me tempted to buy some other older players

On build quality side, I wish the hm901r was fully metal, anyway, sonically, HM901r is actually much much better than i expected, you will enjoy this combo a lot, if i tried hm1000 silver and hm901r and to decide to keep - it would be hm901r.
The battery swap requires opening it, im not sure if its dual battery but I suspect it is as voltage on rails is high (which is very good!). I would not worry about battery IF you just do one thing: never charge it while it is on, it will switch on when you plug to charge but just switch it off. Using while charging ALWAYS puts stress on a battery (unless some nice circuit used but i dont trust it). I have players with batteries 10+ years old and still are great by keeping that rule.