I am having a similar issue. I have a 2007 M roadster.
This car came with the top hi fi with DSP package, verified by VIN. It has the CD player and aux input with a navigation screen. The aux input didn't work when I first tested it, I could not switch to aux with the source button. I also noticed the DSP settings didn't seem to have any effect on the sound, but I didn't really turn it up or test properly at the dealer. The dealer put an aux bluetooth adapter in before I took it home which worked but didn't sound great, and the DSP settings still did not have any affect on the sound. I noticed that the sound is a bit better with CD/radio, but I still felt that it lacks in bass especially and the DSP settings on the navigation screen do not seem to work. I was surprised because I thought the top hi fi with DSP would sound better. I figured maybe the Bluebus would help, so I bought one of those and had a friend help me install it. We also removed the aux bluetooth adapter from behind the radio and everything works. The sound is definitely better and matches CD quality, but it still lacks in bass, and the DSP settings still don't work. The bass/treble settings in the tone menu do work, but the DSP settings do not. I can hear sound coming from all 10 speakers and I can feel them moving when I turn it right up. The mids and highs do get pretty loud, I am just surprised by the lack of bass. I turned up bass and turned down treble in the tone menu and it sounds a bit better but still not as good as I'd like. I know it is a roadster and these are only 6.5" subs with 10ohm resistance, but I thought top hi fi would sound a little better than this.
I've done a lot of research and it seems the DSP amps are finicky and do break often due to water damage. I can't tell if the bass is lacking because of my non working DSP settings, or if this is just the nature of the M roadster?
I love the car and I love the sound of the engine, but I am a big music guy and I love cruising with the top down to loud tunes. I can't decide if I should try and upgrade the speakers, or if it's just the amp. I've also read that aftermarket upgrades can be very difficult with the top hi fi setup.