I am having difficulties playing music when connected through a jack to my stereo. I do get sound, but the volume is very low (the volume on the phone is at 100% capacity). My previous phone (HTC Tilt 2) worked perfectly, and the volume at 5 was pretty loud. On the Inspire, I have it turned up to 10 (the maximum) and it isn't very loud. What "box' do i need to check to make it work properly? It works like a charm via Bluetooth on my car stereo, though...???
No check to make it better as far as I know. What I think you need are self powered speakers, because of using the head phone jack, all you are getting is "head phone" power from that jack. This is just a thought on my part.
Inspire owners are still waiting for the Gingerbread update, correct? There is an app on the Market (actually free on the dev's website) called Volume+ (but it only works on Gingerbread). It doesn't give a huge volume boost on my Desire Z, but it does help some.