Well, since you already own an RD 700 SX (with two expansion slots) you might want to check out the SRX 09 World expansion board and maybe you will find what you are looking for.
http://www.rolandus.com/products/details.asp?catid=13&subcatid=55&prodid=SRX%2D09

By the way, how do you like your RD 700 SX?
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Korg Kronos 61 and PA3X-Pro76, Roland G-70, BK7-m and Integra 7, Casio PX-5S, Fender Stratocaster with Fralin pickups, Fender Stratocaster with Kinman pickups, vintage Gibson SG standard.