I want to run a Rel sub from my integrated amps "pre out" and the sub has only 1 "low level" and the "lfe" input. Do I need an adapter from stereo to mono or do the low level and lfe inputs on the sub act together as left and right input?
My suggestion is connect the left and right pre-out from your integrated amplifier to the input of a stereo to mono converter, and connect one of the mono output from the stereo to mono converter to the low level input on the subwoofer.
The LFE input on the subwoofer bypassed the internal low pass crossover, it is only useful for AVR/processor LFE or low-pass sub-out connection and not suitable for integrated amplifier’s pre-out.
I hope this answers your questions.