Can I replace the Bose Headunit with an aftermarket radio?
Short answer, No.
Here is what Bose say:
Q 7. Can I connect another radio to my BOSEŽ sound-system?
A No. Each BOSEŽ automotive music system is completely integrated, with every element custom engineered to work as a whole. If you install a new radio, the results could include decreased sound quality, incorrect bass and treble balance, distortion at high volumes, and a loss of bass at low volumes.
In the Omega, the Bose amp expects proprietry levels and has a unique response curve. Additionally, you cannot connect the aftermarket headunit directly to the Bose speakers, as they are 2ohm, rather than the industry standard 4ohm.
Can I use my MP3/gayPod player with my Bose system
The only options are:
Cassette Adapter (CCR800, CCRT700, CCR2006, CCRT2008 only)
FM Adapter (all headunits)
Omega headunits do not have a proper Aux in, only a lo-fi mono input just for phones. Unsuitable for hi-fi audio.
There are no 'bypass' units available suitable for Omega Bose, nor any CD Changer emulators. Given the age and that Omega Bose isn't that common (unique to Omega), its unlikely anyone will develop such devices.