The CDTV is the same as an A500, except it also has two additional ROM's that have the code to handle the CD interface as well as the startup screen that is seen when you turn in on. It does not have the side expansion slot or the trap door expansion slot that the A500 has, so although there are a lot of similarities between the capabilities of the CDTV and the A500, they are quite different, so not every hardware add-on for the A500 will work on the CDTV. As for changing out the CD-ROM device for one that does not need the CD caddy, the controller in the CDTV will only work with the device that Commodore installed in the CDTV. I had tried to install an AdIDE controller into my CDTV at one time, so that I could add a hard drive, but I had some problems and have not worked them out yet. It should work, and if it does, you could connect a standard IDE CD-ROM to that, but it might then prevent you from being to use regular CDTV games and programs unless you have a program that converts an A500 w/CD-ROM into a CDTV.
Yes, I know about these Boot-ROMs. I've seen that an A500 accelerator can work with the CDTV, although the case will not close entirely.
And how about clockport hardware? Can I use one in the CDTV? I think yes, but I will miss the extra memory module from Elbox in this way.
I want to add a hard drive, so I'm thinking to find a SCSI controller for that job. Although they told me that I can put CF card in front of the CDTV panel (with SCSI to IDE and then with IDE to CF bridge, something like that), so I can use the CF as a hard disk.
