You might want to check out
DredSensor. It's a similar concept, and I have had good success with it, including on recent Rhodium 6.5 ROMs.
In particular, as long as I only map 'Double-Tap' actions onto the Home/Back/Send/End (double-tap, not double-click) then there doesn't seem to be any interference with other phone/button options and configuration. If I map any other functions like a hard click, or a long-press, then the Dred settings seem to override some of the other phone-configured ones. So, I only use it to map these 4 actions, but it works:
Double-Tap Home - LOCK
Double-Tap Back - CAMERA
Double-Tap Send - Brightness to 100% (Mortscript)
Double-Tap End - Brightness to 40% (Mortscript)
Might want to try it for your volume issue...
EDIT: I just tried Showcase as a task manager, mentioned above by jmorton and below by apinkel, and holy cow! That. Is. Awesome.