96 kbps is rather little for an MP3 audio stream and 128 kbps still isn't quite enough, and I'm sure both of them will be inferior to good FM reception. You may get a wider frequency range (FM won't go over 15 kHz) but the coding artefacts will be audible.
Quality of WMA can be better depending on the codec, but generally it will still struggle a little at 128 kbps.
128 kbps can be quite good with AAC/AAC+, which makes better use of the bandwidth. I don't know if BM5 supports that, but if you have a computer connected to good speakers, try out the different streams offered at Radio Paradise. The 128 kbps AAC stream is great as they say - MP3 will need 192k or more for similar quality.
Of course the quality will also depend on the station itself - some manage to destroy the sound already when transmitting, be it over the air or over the internet. Different encoding software will also create a different result, even if the final bitrates were the same.