Which firmware are you using? Latest beta FW is very responsive, but I believe one before, which I skipped, did make screen rather unresponsive. I have not changed the screen protector but do try to keep it nice and clean to help avoid any phantom swipes. Line Out has an adjustable volume which is remembered separately from the phone out volume (which is great, I accidentally blasted my ears too many times on my DX90!). Make sure it is set to 150. I do not think the gain should have any effect on line out. I use Mango OS rather than the Mango player on Android mainly because the album order is correct, although some people report they also hear the better sound quality. The UI is very responsive except for delay in swiping between screens horizontally, which Paul has said will soon be fixed in FW update. To change to Mango OS select it as option when powering off in Android mode. Hope this helps.