Recording in multitrack mode has very poor quality since using ASIO

Hey all!

My recordings and coming through on Audition very distorted. I've attached a file which hopefully will demonstrate. 

So I've got Audition on a ASIO using ASIO4ALL. ASIO4ALL has a Behringer UMC404HD plugged in to it and is outputting the 4 channels to Audition. In mutlitrack mode I have inputs 1 and 2 (the music) in track one as stereo, and then mono for input 3 (mic 1) and mono for input 4 (mic 2). 

ASIO4ALL has latency of 32 samples, hardware buffer offset at 10ms and always resamples 44.1khz to 48khz.

In Audition I have selected on the Audio Hardware settings page a buffer sze of 512 and a smaple rate of 44100.

I'm on Windows 10.

Can anyone suggest where I might start trying to get these recordings sounding usable?

Cheers!