I've tried connecting my stereo or other similar device to the headphone/mic output of my N800 using a cable with a 3-pole miniplug; however, the sound level seems reduced. What would be the best way of doing this? Am I harming the N800, since the headphone/mic cable that comes with it has a 4-pole plug? I've tried using a 4-pole miniplug to 3-RCA adaptor (2 audio + video) but get no sound at all on the audio RCAs.

I use a standard 3.5mm stereo "Y" cable... 3.5mm 3 pole stereo plug (headphone plug) on one end and two full size phono-RCA connectors on the other. The tablet doesn't have a lot of power to offer (it's designed to drive headphones), so the volume level coming out is probably lower than other devices (the tablet volume even at max is about 1/2 -2/3 of the volume coming out of my laptop jack) but that's to be expected given the size and power features of the tablet in comparison. So yes, the volume will be a bit lower, but no, it's not damaging in any way.

Thanks for the information.

Regular headphone jack. XMMS. All good.