The CF to IDE adaptor arrived today, and here's what I found:
I plugged it in to the MyIDE along with a 64MB CF card I had. I boot the Atari and run scandisk...it recognizes a drive as being attached, and passed the scan...no problems. I then run fdisk, and again, it detects the drive. I set up a 16 MB partition, and go into MyDOS to set it up. It recognized a high-capicity drive on drive 2. So I initialize it, do a disk directory, and it shows free sectors! I then write DOS files to it, and they write.
I then run fdisk again, set up the partition as drive 1, and boot directly to the partition on CF!
So I've decided to build the CF adaptor into my 800XL...it's smaller and will use less power than a hard drive. And I can cut a slot in the back to change CF cards as needed.