Switched amp for AUX port with Aftermarket stereo?

[CtrlAltDefeat]

I installed an aftermarket stereo in my 2008 LB and I really miss my aux port. I was thinking it might be possible to install a small 4 channel amp behind the HU with some sort of A-B switch to switch between the HU and the AUX port. (Ideally the amp would be switched to and turned on when signal is detected on the AUX port, but no idea how that would be done.) Any one have this setup or have any suggestions how this would be done? I would appreciate any help;
Thanx

[sqcomp]

...ummm, maybe I'm oversimplifying this but why don't you just get a source unit with a USB input?

Most decks now come with them.

[CtrlAltDefeat]

well I already have a HU that I like... If I can't find any thing that works for the AUX Then I'll consider buying a new one, but generally I dislike having cords or other things attached to the front of my HU...

[awdblazer]

what kind of deck is it? does it have rca input?

[sqcomp]

You need to remember that there are plenty of decks out there with rear USB inputs.

Heck, there's also Bluetooth connections now...not that the sound quality is anywhere near acceptable though...

[WolfWings]

Hell, there's CB Radios with bluetooth on them at this point to couple between devices with.

[CtrlAltDefeat]

well I used my older HU from my last car and I was hoping to try this as a stop-gap measure alternative to buying a whole new HU.