If you are a bonafide independent contractor, not a partner or part owner of the band, asking you to front the CD by investing is inappropriate, imo. If you are a partner with ownership percentage, then I view this as normal.
However, I would ask to re-record the bass tracks and remix on at least one song. This assumes they have all the original tracks. Alternately, you can add a couple of new tracks with the current band to include.
One thing you did not touch upon was who receives the profits from the sale? Are you included? Or, does the proceeds to fund band assets? Perhaps, it's meant to break even, or be a loss for promotion?
If I was in your shoes, I'd want answers to these questions... particularly if profits fund band assets, and what percentage of band assets would I own. Plus, how are these assets handled during a severance or separation from the band.