I have an 03 MCS with HK, NAV and 2-spoke MFSW.

My Boost head unit is stuck "on" and no buttons or controls will work
except the volume. It also will not eject the CD that is in it.
The navigation voice works and there is no issue with sound quality
from all speakers.

Any ideas?

If it really turns out to be an issue with the head unit, my first thought
is to replace it with an aftermarket unit.

Is there any way I can retain the HK, NAV, and 2-spoke MFSW controls?

Please advise.

 

You can go aftermarket, but you'll need an adapter (newministuff.com has them.) You can easily get an OEM replacement for less that $100, so unless you're pining for a particular aftermarket item, OEM is the most cost efficient way to go.