Instead of using adapters, why not use 1/4-inch to RCA cables. They're available at some music stores, and I believe I saw them at Radio Shack as well.

Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!

K+E=W (Knowledge Plus Experience = Wisdom.)