I had an idea today to buy a cheapish tube amp from aliexpress and running it through Babyface pro for some sound colouring, has anyone done something like that and what was your experience?

Also by tube amp I am not referring to guitar amps.

 

I am summing through a Mackie Console with an ART MPA Pro II run through the master bus insert. It added some depth and nice color. This one is still running the stock Chinese tubes. I've also got one in which I've just replaced the tubes with some Mullards. I haven't summed with the Mullards yet though.

 

The Mullards will make a difference. The unit should be a little quieter and everything that you like about the Pro MPA II will be slightly extended.

 

I had to replace the tubes due to one side becoming microphonic. It made more sense to me to put in a matched pair in the event that I use the unit for stereo operation.
I did do some female vocal tracks with the Mullards. They seemed like they gave the track more heft then the stock tubes did. It's nice having two units with slightly different color. I can't wait to run some guitars and drums through the Mullards.
I may run the summing through the Mullard unit just to give it a try.