Anybody use a single ended component with one that is balanced?

The OP is talking about running the XL output from the pre into the RCA input of the amp.  That will produce sound.  It may not be optimal.  

OP should use the RCA outputs on the preamp if it has them.  Or use a Henry Engineering Matchbox or a Tascam adapter. 

Yes the pre has them. So it would be rcas from the amp, which is all it has, to the rcas on the pre, which has both rcas and balanced.

I could also use the neutrix adapters which avanti above suggested. 'At the amp I use a neutrik female XLR to male RCA cable adapter.'

Oh OK. Yes, just use the RCA (aka "single-ended") connection from the pre-out to the amp in. Don’t use the XLR outputs on the preamp until you have an amp with XLR inputs. You won’t get optimal sound by just using the jack adapters - or at least that is a possible risk.

BTW: I like the XLR adapters because they always connect ground first, so they can be swapped live.  I built a patch bay to switch between preamps and amps with neutrik jacks. Better than a HT bypass! 

@jji666

+1 Don’t add an adapter. If the amp is balanced it a;ready has one and is likely to be of higher quality. The manufacturer has a vested interest in making both inputs sound good.

Many people think XLR is better port. Do you think of Conrad Johnson pre and amp? They always use RCA port and so many people love this brand.

I might enter this brand some day if it works well with audio research power amplifier.