I've had to have a two day break from this thread because I decided to try my two hard drives on the JMicron interface and the DVD drive on the Intel interface. The mainboard manual says the JMicron interface supports up to 2 devices.
The short version of the story is that I ended up with the file systems on both drives comprehensively trashed! Linux is normally very good at recovering from file system errors but it couldn't do anything with these.
The long story: After swapping interfaces I booted the machine using a Knoppix v5.1 CD, because I'd need to change device names in a couple of files, but went into the BIOS first. The DVD registered as the first primary drive in the first main menu screen as expected but it seems very odd that once in the BIOS any devices connected to the JMicron interface are not listed anywhere. Drives are set as Master and Slave.
They are shown, briefly for about 5 seconds, just before entering the BIOS and it was here that I noticed that only one hard drive was shown after the heading 'HDD:' but the name that followed was just a random collection of letters and numbers, the font was also broken up (characters had gaps in them), and that line of text was flashing.
I left the BIOS and continued with the boot into Linux and tried mounting one of the partitions. On seeing the message that 'the filesystem has errors' I didn't go any further but closed down the system.
I then swapped the cables back to their original positions and tried to boot but it hung a short way into the process. I decided to swap the primary drive and DVD drive back into my old machine and boot from the same Live CD to examine the hard drive. The contents were basically rubbish! I spent quite a lot of yesterday restoring from tape which, as there is a fair amount of data, was a rather slow business. The tape was up to date as far as early yesterday morning so I lost a couple of unimportant emails but that was it.
So I'm not over impressed with the JMicron interface so far.