This is a great way to get your equipment off to the side and leave the amp between the speakers. I used this setup once, i could sit in my chair and have access to all my sources and volume control with out a remote:-) using a 30ft high quality RCA cable it worked very well with my MAC preamp into a 300watt per channel MAC power amp driving a pair of Mirage M3’s. I would contact Signal Cable they are in New York and they make cables that are excellent sounding and affordable, just call them and they can whip up a nice long XLR for your needs, Much recommended.
P.S. I use their MAGIC Power cables and Sennheiser Head Phone cable and Subwoofer SPKON cable for my REL B2 sub, These are all custom made.
Matt M