I used a 1680 on a couple full projects. The last one was tracked on a 1680 and I tried mixing on the 1680, which is what I did the first time. It was a pain trying to edit and make the automated mixes that you will be looking for. So I took all the effects off all the tracks to get to the raw signal, burned them all as separate tracks to a CD and moved them to a laptop for editing and remixing. Pain in the a$$, but it changed my world!
The 1680 was a great idea when it came out, but it has been surpassed as far as a true CD creation tool. It is too limited, not to mention they didn't give you any way to bounce your tracks to a computer for editing. It can do well in a live setting, but only records 8 tracks at a time. BTW, it records in 20 bit, but all effects and editing are done at 24 bit.
If I were you, I would look for a standalone unit that has a USB out, or something similar. Then you could record the tracks using your stand alone unit and bounce them to your computer for mixing and editing. You could probably use your current computer setup to do this. Grab N-track or something like that, some kind of moderately featured software to do all your editing, effects and burning. Look on these boards for the free options of effects and software, I can't remember their names off hand.
This option would give you the greatest flexibility with probably the least cash outlay. Or you can do what I did.....
Buy a powerful laptop coupled with a Firewire soundcard that allows for 16 simultaneous inputs (using an additional Behringer ADA8000 rack pre). Then you've got a powerful mobile production setup....but you'll be out atleast $2500 for that.
Check out standalone units that record in 24 bit that don't have a lot of effects or editing options that have some sort of USB or similar out. That's your best bet, IMHO.
Jonathan