Tom, I don't use Realtrek so I am not sure exactly how to set it up for recording. However under settings/sound there are a number of options available. The first one has to do with inputs. I would check each and every option available in all categories. Again I don't use RealBand but make sure that your RB audio and MIDI settings are identical to Realtrek. Since you can correctly record in BiaB I suspect the problem is with RB.

To be honest the best thing you could do is to invest in an external audio interface. In all probability the drivers in an external audio interface would easily solve the problem. I know in my old Win 10 system many times I have to change the driver settings to get correct MIDI recordings; that happens with a lot of MIDI tracks and effects.

I hope this helps and good luck.

Whenever I get something stuck in the back of my throat, I dislodge it by drinking a beer.
It's called the Heineken Maneuver.

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware