Thank you for confirming.
Yes, the newer models are different, the new systems no longer have a hard drive, and generally don't even have an optical drive any longer. Optical/disc technology has been considered obsolete for many years, as everything has transitioned to digital storage and on demand services.
There are some other options for replacing your system. Honestly, I would not personally recommend another bose system. Their parts are highly proprietary and grossly overpriced for what you get. For a fraction of the cost you can get a better quality standalone AV receiver and subwoofer, and pair your existing bose speakers to it to avoid rewiring and mounting new speakers. The speakers you have are likely fine, the fault is in the main unit or acoustimass module.
As for your discs, I would recommend "ripping" them all on a computer to a mp3 format, then storing them digitally on a computer for remote/network access, on an ipod, etc which you can play back through a new receiver system.
I can give you recommendations on specifics, if you'd like.