There was an issue with Reaper not handling wma files well as it was using ffmpeg decoder but the very helpful guys over at Reaper implemented the Windows Media Foundation codec to fix this issue after I asked them and I did some testing, now Reaper plays wma direct accurately on old or new hardware.
You will need the latest version from 6.57
It now plays fine on a 1.9GHz Celeron Win7 laptop with a 5400rpm HD.
Thanks to the incredibly helpful guys at Reaper this shows what I have been saying about Biab/BBPlugin/RealBand playing source files direct that seemed to fall on deaf ears around here.
All this would allow Biab to be used as a Live Arranger that will be a game changer, the Reaper guys saw this, I just hope the Biab guys will also now see.

Band In A Box Track Injector for Reaper

It will give you way more control of what you need as it's loading the source files directly (wma or wav) into Reaper without waiting and creating wav files.
You can easily add multiriffs to any section of Reaper's track instantly without having to render a lot of wav files.
You can change any section at anytime.
Any item you click on will show what RealTrack section it is allowing you to see what instruments changes there are on any track instantly.
Any items can be extended either way to give custom variations as you don't have one consolidated wav file.
Shots and Holds for RealDrums can be custom selected by extending/shortening the Hold/Shot section for another variation.
Shots and Hold for the RealTracks can be adjusted easily in timing or volume level.
RealTracks can be changed from Direct Input <> FX version with one click keeping the same playing.
RealDrums can be split to stems (where available) instantly after you have made any custom adjustments to the stereo drums track like adding fills where you want.
I don't know why the Stems don't have the shots n holds at the end of the file same as the stereo files ???? so any shot, holds or pushes you have changed you will have to copy from the stereo drum track.
The Tracks from Biab will adjust to any decimal tempo map in Reaper.
It can have 4/4-3/4 time signature changes.
With so many pre made Styles in Biab this allows you to create you own unique Style or pick a RealTrack instrument or Drum randomly that will match the Feel, Time Signature and tempo range it is set to.