Most Realistic Sound Settings

Hi - I bought FSX when first released but found, like many others, that my PC was found wanting in many respects....I am now at the point though where I am using FSX with decent quality and framerates and want to try and make the experience as realistic as possible.

So - the simple question is - bearing in mind I am using default FSX sounds (apart from that revolting main menu music!!), what are the most realistic sound setttings to use? When FSX is installed, all sliders are set to 50%, but I'm pretty sure this ain't right!

I know every system will differ, but I have nothing to compare it to since I've never sat in a real flight deck and would appreciate advice. I am using a 7.1 sound system, if that affects the answer.

Also, I know there are a few sound add-on packs out there....would appreciate opinions as to which ones, if any, are any good.

Greg