Adding one subwoofer to two sets of speakers

The situation: I have speakers (M-Audio BX5a, with a XLR and TRS inputs in the back) hooked up to my computer, and a Vizio soundbar (spdif and 2 RCA inputs, and a sub out) hooked up to my plasma for playing games. The BX5a is connected to my laptop via a USB DAC, the Creative X-fi HD. Everything is in very close proximity.

What I want to do is share the single subwoofer between the speakers and soundbar (with neither being used at the same time). Would that work, and if so, what outputs should I look for in a subwoofer? I'm really new to audio and have a difficult time making sense of all of the different types of connections. Any suggestions for a good cheap sub are welcome.

Well, the BX5a only has available XLR inputs (using the TRS to connect to the RCA output of the USB DAC). No RCA on the BX5a, so I don't see how that would work.

I suppose I could use this (http://www.amazon.com/PPRC-X05-Professional-Audio-Cable-Female/dp/B000V1RLI2) to connect the XLR on the speakers to the RCA output on the sub. The other question I have is, how would I connect the soundbar to the sub? Using the speaker level input on that unit? What cables go into that, and could the speakers and the soundbar be simultaneously plugged in without causing problems?

I don't see any subs with more than one RCA output. Being that my Vizio has a sub out, I'm guessing if the subwoofer had an RCA output and a sub in, I could use the above cable to connect my BX5a to the RCA and another cable to connect the soundbar to the sub in...? Something like this? 

EDIT: would this work:http://www.crutchfield.com/p_107PSW110B/Polk-Audio-PSW110-Black.html?search=polk+subwoofer

More than I want to spend, but If it works, I'll look for something with similar inputs. These things are difficult to find.

Quote:

Originally Posted by adamlau 

USB  DAC > TRS to RCA adapter > RCA Y Adapter  > Sub > RCA to TRS adapter > BX5a. 

Where does the soundbar fit into this?

Sure.

This is the vizio soundbar, connected via the SPDIF to my Plasma.

My BX5a has a XLR and TRS, connected to this USB DAC via the line out

Quote:

Originally Posted by adamlau 

Post up a pic of the available outputs for the Vizio, including the sub out. Or mention the model number.

Oh, I was a bit confused how the Y adapter fit into the Left/Right inputs without knowing that you only need to plug it into one of them. : /

Ok, here's another question...can you plug one Y adapter into L and one into R on the same line in? For example, could I use this (the single line in), plugging the Y from the vizio into L, and the Y from the DAC into R?

If you need two SETS of line inputs, I can't find many (inexpensive) subs like that. Suggestions?

EDIT: and do all of these adapters degrade the audio at all?

Quote:

Originally Posted by adamlau 

Vizio > Sub Out (RCA) > RCA Y Adapter Line In # 1 > Sub
USB DAC > TRS to RCA > RCA Y Adapter Line In # 2 > Sub > RCA to TRS adapter > BX5a

Line in and line out...would this work? It doesn't have the LFE input.

Also, I tried to visualize your setup in my head, and I don't understand why I need so many Y adapters. I can see why I'd need one to connect the vizio sub out to the line in on the sub, but that would require only one y adapter, as I could still connect the other end of the RCA to the Left and right sub input. This image is how I see it working, what is wrong with it:

Or is there another reason for the Y adapters?

bump

SO I got a sub with a line in and a line out, and I can't figure out how to connect it based on that sequence:

Vizio > Sub Out (RCA) > RCA Y Adapter Line In # 1 > Sub
USB DAC > TRS to RCA > RCA Y Adapter Line In # 2 > Sub > RCA to TRS adapter > BX5a

Again, why do I need the Y adapters?

Any help is appreciated!