Really? Which A/V companies are allowing software hacking of features such as surround processing and/or speaker configuration?

Any one based on a Linux platform and conforming to the GPL. TiVo comes to mind, though strictly speaking that isn't an A/V company.

RokuLabs, which makes an HD playback device (HD1000 a.k.a. Photobridge) is another, though the Photobridge (don't let the name fool you, it will play HD MPEG2 video streamed from a PC, PS and TS) only has digital and two channel analog outputs.

Finally, there is a bunch of free (as in GPL) sofware available to do DD decoding on a fast enough PC (not requiring a DSP), though that starts to run up against possible patent violations.

As for adding a centre not destroying dialog imaging, I disagree. I don't want the dialog 1/4 of the way right from the centre creen to appear at the centre of the screen. Stereo miking works fine for the sweet spot.