Im not so sure that the external drive wont work..... have a look at the iDVD and DVD studio pro forums on the Apple boards - I seem to recall that a few people have the pioneer going externally.
AS for the DVD-ram drive. i am keeping mine becaue it gives me so much flexibility with back up , and I have a DVDram camera that uses 8cm dvdram discs - neat! <a href="http://www.softarch.com
</a> are about to release an upgrade for their DVDram Tuneup pro which will allow me to convert the mpegs on my DVdram discs to QT. of course, this is easy for me to say as I also have a 867 with the super dirve (the best of both worlds).
Unrelated, but combined with the above, Panasonic have brought out a set top DVD recorder whcih records DVDram, DVd-r called the DMR-E20. There is even a new model in decembe called the DMR HS1 which is the same and has a 40gig HD too. With the Softarch software I will be able to record DVDram from TV, then put it in my Dual 500 and watch/edit the program too. Kind of neat.