Radio shack sells rca to 1/4 inch converters. Run rca into the DI (you will need a stereo DI box. Run the rcas from the sp to the converters to the di. Cost you about 3-5 bucks. (Not including the DI)
The sp is a rca beast, thats it but with good rca cables and a nice di box it'll sound fine. I don't think you should even need the di box. I run the sp into a fender passport PA direct with no DI box.
yeah im pretty sure you dont need the DI box, unless you were running the sp through an amp that you wanted the sound/color from and you wanted to come out of the pa instead of a speaker cab
yeah, I just use a 12 foot Hosa dual RCA to dual 1/4" cable most places i play. If you can avoid running your equipment into XLR jacks, do so.
However, sometimes you're playing a venue and they've got a cable snake on the stage floor, and the only open jacks are XLRs. So you do what you gotta do.