The Phenom 955 is a very good quad core processor which has unlocked multiplier,So you can above 4ghz using nice aftermarket cpu coolers.
But since you have not finalized and considering that you are going for the amd then the1090T is the best option you can get from amd.It is a hexa core black edition processor along with turbo core.Well many programs might not still use more than 2 to 3 cores effectively but you can expect softwares with more threads in the future.Under that cases a 6 core will outperform a quad core.If you can't afford a 6 core now then look out for the amd's zasma(4 core with 2 cores disabled) with turbo core(also with a good unlocking mobo and a little bit of luck you can turn it into a six core).With more cores you can do video encoding faster.
What I'm looking for in the motherboard:
Comes as close to the 4000Mhz Hyper Transport FSB on that Phenom as possible
i did not get what you meant here above
The phenom officially supports max DDR3 1333Mhz ram.So i would recommend going for the good lower 1333Mhz ram with good overclocking options.
Actually the phenom does not require DDR3 as a requirement,only the intel i series(probably i7 or higher)processors need DDR3 as a requirement.
Still go for a DDR3 as prices are falling and they provide a larger bandwidth.
Almost all onboard sound solution comes with 7.1.So it's just fine.
Well since you haven't mentioned your use with the computer, i can't recommend something.