I was originally going to french this remote speaker into dash upper tray so it would sit flush with rear portion of tray just below center speaker but I ran out of time. So for now I used the include mounting bracket and surface mounted it to the tray. I can remove the speaker and bracket easily for times I'm not using radio. I might also look into tying it into factory center speaker, just not sure how to do that yet.
I don't think you'd be able to connect the center channel speaker very well. First you'd have to disconnect the center channel from the main speaker system, which is not hard to do, but would likely cause your stock stereo to sound rather poor, since it expects the center channel to be there.
The second problem is that the signal coming out of the race radio isn't amplified, it looks to be around 4W max. The external speaker you have is designed to work with that wattage, the same way headphones will work without an amplifier. The center channel is not. It may work, but I would expect it to sound no better, possible worse than your current external speaker.
You would also need to splice the wires to get it connected correctly, which would be kind of a pain to do. If it were me, I'd probably by a second center channel speaker for $30 so that I don't have to worry about splicing it back to the main sound system if it doens't work.
https://www.tascaparts.com/oem-part...tMTUwJnk9MjAxNyZ0PXJhcHRvciZlPTMtNWwtdjYtZ2Fz
Of course, the alternative to this is getting an external amp between the radio and the center channel, which will cost in the $100 range plus additional wiring.