TOPIC:

When I import my REW files into the miniDSP software it distorts like hell. Any ideas what I'm doing wrong?

Difficult to reply to your question without more information.

Could you attach the REW measurement file (filetype of mdat)?

This is the mdat

mdat as zip file

Thank you for the useful information.

I am going to assume that you have loaded the REW filters correctly into your miniDSP and comment only on the mdat file.

EQ filter 1 (23Hz) is a 11dB boost to a speaker that is probably not capable of performing that low?

EQ filters 4 (67Hz) and 5 (82Hz) look to be an issue because you are attempting to boost by 9dB what is potentially a room null. Nulls are usually the result of frequency cancellation and boosting does very little to resolve them.

The distortion is probably the result of your speaker being driven beyond its' capability.

Removing these filters should stop the distortion.

Moving your speaker(s) may reduce the null.
You may like to use the REW room simulator to check if you can replicate your current measurement and then simulate other speaker positions before physically moving your speaker(s).

nb - you may find it easier to interpret the REW graphs if you add smoothing to your measurements. Var smoothing is often recommended.