Mobo+CPU+RAM upgrade

I've been running the same system give or take a disk drive or two for the past 3 years.
Here are my old specs

Sunbeam Transformer Full Tower Case
ASUS A8N32SLI Deluxe Socket 939 Motherboard
Athlon FX52 CPU running stock 2.4Ghz
4x512MB Crussual PC3200 stock timing and clock
BFG OC7900GS 256MB GDDR3 OC out of the box
2x 160GB WD 7200RPM SATA/3GB Striped RAID OS partition Windows 7 RC1
60GB IBM 7200RPM IDE Video and Music
80GB WD 7200RPM IDE Video and Music
IDE DVD-RW and IDE DVD-ROM drives
A floppy drive
700W PCU

I'm looking to replace the Motherboard, CPU and Ram at this time. Graphics is a later deal as most my gaming is on my PS3 now, and the PC games I play aren't heavy enough to call for an upgrade.

The hard part in my upgrade plan is that I've got a set of musts that need be met.

1.)The Motherboard must have S/PDIF out with Dolby Digital Live.
2.)The Motherboard must have room for my Graphics card, an extra IDE controller card and my DVR card. If the Motherboard doesn't have Firewire, then add to that room for a PCI card.
3.)A Quad Core CPU. I'm thinking Athlon II x4 socket AM3 or comparable.
4.)The CPU and Motherboard must support Windows 7's Visualization for XP mode.

I'm looking at spending about $300

Please help. I'm working 50+hours a week and spend what time I have off writing and drawing for an ongoing story.