Use two audio sources at once in linux?

I'm running Xubuntu on a brix while outputting video to two 32in tv's. They are not mirrored, just a normal dual display setup. I currently have one of them outputting audio but was wondering if I could output both at the same time. I haven't seen any options so far but I'm sure if it's possible linux would be the one to do it. I should also mention that one is HDMI and the other is miniDP to hdmi. I don't see an option for the mini dp to hdmi cable to enable audio at all but video is working fine.

It's likely possible, I haven't toyed with Linux audio in a while.
DisplayPort specifications have parameters for audio, but your DP port would have to support sending audio. I'm not sure that a DP->HDMI adapter would keep audio even if your port supported it. Though that may depend on the Adapter.

PulseAudio Preferences (Paprefs) is exactly what you need.

Here is the Link to the Launchpad

And the Ubuntu Apps directory

Let me know if you need an help configuring it.

im not sure how you would go about it in linux and have never got it to work with digital audio though I use analog so it doesnt bother me, A lot of mobo's nowa days have audio pasthrough and if you could potentially capture that audio(record) and redirect it to your digital output, that could work?
Just an idea

I've seen that and tried to enable the secondary audio but the mini-dp monitor isn't showing up in the audio settings. It might be because the adapter I'm using isn't active. Might have to order a new adapter.

Make sure you restart Pulse Audio by either logging out, rebooting, or running pulseaudio -k