I use female RCA to male 1/4" jack adaptors. But considering I use the cable for all my ins and outs I wish I had used RCA jacks. Though one down side is RCA's will protrude out and 1/4" jacks do not.
The reason I use the Isolator for both ins AND outs is cause if you remove the cable from your amplifier while everything is powered on you can blow your SID, Furthermore even if you wait until all is connected before powering on your gear, some old (and even new) amps will create a voltage spike when powered on that could potentially be lethal to the chip. SID's are very fragile and taking every precaution to ensure it's safety is worth it to me. Especially after having blown 2 SIDs before.