Haha, I too have the Promedia 5.1, which I will sell off once my upgrade is done.
I really have no idea, but I'm not sure if the 819V would be the best choice for running towers in a HT, as it's amp is on the
weaker side. I don't have hardly any experience with receivers, other than the one in my sig. Which maybe isn't the best for it's price, but it gets the job done.
As for the mobo. I'm not sure what you're trying to do exactly. If you want to connect your receiver and z5500 to it, that's easy. Since your board has both optical and coaxial output you could use one for the receiver and one for the z5500. Or you could connect the z5500 using the 3 analog connections. I think this would work, if that's what your trying to do. Though figuring out your PC's sound settings may be tricky. It was down right maddening for me.