I currently have a behringer umc202hd audio interface and I'm looking to upgrade to a usb mixer (behringer xenyx q802usb). I'm doing this to give myself more mic inputs however, I don't want to waste my audio interface and I don't want to spend much money on a mixer. So, my question is can I use the audio interface's 1/4 inch outputs to lead in to the mixers line in to give myself in theory 2 more mic inputs?
So, my question is can I use the audio interface's 1/4 inch outputs to lead in to the mixers line in
Actually, with that interface, my guess is that you probably could by using the direct monitor switch (i.e. not having the audio go in and out of the computer). It's quite a sneaky idea! It would be a slightly odd setup though and I would imagine you're slightly increasing the chance of strange noises and hums creeping in by having two devices connected to the same USB bus and also connected to each other through an analogue connection.
to give myself in theory 2 more mic inputs?
As per our conversation in the comments - it depends what you mean. It gives you a place to plug 2 more mics in, but even if it worked, you'd still only be able to record the mix of those mics, rather than the individual tracks - which might be fine, until you realise you want the individual tracks!
If possible, you might want to look at selling the umc202hd and getting something with more inputs like the UMC404HD (which would give you 4 individually-mixable inputs) or the UMC1820 if you really need a lot of inputs.
If you really don't think you'll need to mix the tracks separately in the computer and you are otherwise happy with the UMC202HD, I'd suggest perhaps looking for a nice second hand analogue-only mixer (with no USB) and using that with your existing interface.