192k will be fine for what you intend; headphone listening will be the only medium where you'll notice a big difference (assuming good headphone rig). I'd just throw my favorites on there in 320k variable, or lossless, and leave everything else 192k. You can do that on a need-to-hear basis too (assuming you put some lossless faves from one computer over to the other one that will have iTunes/ipod access).
