I have a number of mp3 files in the cbr 160 to 192 range. I want to decode them to wav using a DSP plugin (the excellent crossfeed plugin) and re-encode to mp3.

I know this isn't ideal, but what would give me the best results? Should I re-encode at the original bitrate (eg. cbr 160) or should I use the alt presets? Which would give me the best sounding file?

Thanks.

You said it yourself, but i think it's important for everyone, so i will repeat it: Whatever setting you use, you will lose quality with transcoding.

Now, about the bitrate: The thing about using the same bitrate to somehow maintain the best quality during transcoding is a myth. The encoder cannot detect which bitrate or setting the MP3 was previously encoded in. It will use the same "data-reduction" mechanisms as it uses on original WAV files coming straight from the CD. You can imagine that a former MP3 is therefore quite problematic. To maintain a decent quality, use the highest setting you can tolerate: --alt-preset standard / extreme / insane.

CiTay, I hope the loss in quality isn't too noticable. I'll have to test it out.
I will certainly keep the original mp3s for general use with speakers. The above scheme is so that I can use the crossfeed plugin with a hardware mp3 player (wouldn't it be nice if a hardware player could support 3rd party plugins :-) ).