We made some product changes recently. All the stereo amplifiers now have RCA inputs only. All the balanced mono amplifiers have XLR balanced inputs only. If you need to run a pair of our balanced input mono amplifiers from a single ended preamplifier, we will very soon have a separate small R2X box adaptor. This nifty little active circuit has single ended RCA inputs and balanced XLR outputs. The balanced outputs are active and provide the same output impedance to all signals.