OP wrote:
"I'm running software for audio recording and it's been running very well and is very stable with Mavericks. It's an earlier version of recording software. Since El Capitan is still new, a lot of users of this recording software are having issues"
What DAW software do you want to run?
My advice:
DON'T change anything on the Mac you have now.
If the software runs under Mavericks, it runs.
Leave the internal drive alone.
BUT --
Why don't you try installing El Capitan on an EXTERNAL drive, along with your audio production software?
You can boot and run that way and give your DAW app a "test run" without messing with your current Mavericks setup on the internal drive.
Just because others are having problems, doesn't necessarily mean that you'll have the same problems.
If things don't work out, just re-initialize the "test drive" and try something else.
If nothing works, you could always keep the old iMac around as your "music production platform", running an older OS -- and still use the new iMac for other things...