Hi Mig,
Give the USB adaptor a try, I don't think they were ever the "recommended" way of hooking up the sampler but I think some have had success.
This was the card I used:
http://www.amazon.com/Adaptec-2906-S.../dp/B00005111H
Also, Recycle 1.7 could send samples and keygroups directly to the S3000XL, it was a nice companion to Peak for sample transmission.
Akai also supplied a program called MESA for editing on the MAC (I think it formed the basis for AkSys for the S5000/5000 Z4 etc). Its discontinued so should be available online if you search, I can hook you up if you can't find it (Admins - That is cool I think/hope, as it's end of life/discontinued software now?). I also have pdf manuals and odds and ends if you need them. Also look at
www.chickensys.com for their translator tools if you get really into the S3K.
Happy sampling!
Cheers
Dave