A Y cord. Although, you risk releasing the magic smoke if things disagree with each other in a substantial way.

As long as the power level is low, the worst case scenario is it doesn't work or acts peculiar.

You're feeding two outputs into the same thing and tying them together electrically when you use a Y cord.... but I seem to recall doing something like this when I was younger and didn't have the resources to buy the right tools for the job. I'm still alive and I have all 10 fingers..... so it must not have been a total disaster.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.