With the UFX or a similar multichannel interface REW only knows L and R as inputs and outputs.
So, in the Audio/MIDI application under Configure Speakers choose Analog 1 and Analog 2 as output (software playback). Sound from REW will be routed now to these channels, which in TotalMix can be routed to a hardware output, e.g. speakers. Route these channels to Analog 1 and Analog 2 hardware outputs and use loopback to send them back to REW, which expects input from analog 1 (L) and analog 2 (R), to make the interface calibration. Once the interface calibration is done and stored, the channel routing can be changed, eg to speakers.
To make a measurement, a mic input (Channel 9...12) has to be routed to hardware inputs Analog 1 (L) or 2 (R), e.g. route the mic input to a hardware output and with a cable connection to hardware input Analog 1 (L) or 2 (R). I simply connected an external mic pre to hardware input Analog 2 (R). Now the signal from REW goes through Analog 1 and 2 to Totalmix and from there to the speakers. Hardware input Analog 1 or 2 has to receive the mic signal from either an external mic pre or an hardware output through a cable connection. Voila, REW works like a charm.... Cheers
