You probably wouldn't even need SSD's to stream audio from that machine, set up a RAID 0 with 3 or 6GB/x drives (whatever your board is capable of). I then suggest maping those drives to your primary build but there are other ways to stream.
Intel is the way to go for audio editing. Personally I would look at a Mac for intense audio work but, it depends on what program you are looking to use. Socket 1155 doesn't support triple channel memory, that's why you can't find them. If you think you need a lot of RAM, you can get 8GB pretty cheap for your build but 4GB would be plenty for a good start.
What do YOU mean by "slave" PC? Do you want to use it's power to process as well or simply use it as a dump computer/media/synth box? If you want to use it's power, you will have issues due to AMD and Intel. There ARE ways to set machines up to utilize each's power as one, essentially creating a machine with XX # of cores/processors sharing the work, but, the only GOOD way to do this is with multiple identical machines. Trying to utilize the AMD's power while working on the i7 would likely actually cause more problems. Also, these farms use more than 2 machines. I think you need a minimum of 3 for most of the clients that actually DO this type of work. It is a technology that was pioneered for the movie Titanic, quite an interesting scenario. However, if this is not what you are trying to accomplish, elaborate on what help you want us to provide.
SSD's are essential for sample streaming from libraries like East Wests - Hollywood strings. A mac would be nice because Pro tools runs much more efficient, and Logic Pro is also great. I mostly use Cubase 6 64x so that is not really an issue.
The help I need is the most cost efficient 1 pc.
Right now I am debating whether having a dual cpu, each 8 cores, is better or at least equivalent to having two slave pcs.
This is what I'm thinking about building, in lamens.
-Dual CPU motherboard, they would have to be server cpus and motherboard of course. I was thinking the new AMD bulldozer, but I'm not sure if there is a motherboard that can support two bulldozers. Dual xeon would be nice, but way too much money, for a little more performance.
-I would need over 42 gigs of ram, which I'm sure all dual server motherboards support up to 128, its up to the CPU's to support it. (It is easy to utilize all the ram with these libraries, hard drive bottle necks is my main concern)
-I would also have a couple of SSDs, one for my OS and Cubase 6, the other for my most demanding samples (east west).
-Lastly, I think a good soundcard with at least 800 firewire is in check, this will help with buffering samples. the 800 firewire is because I will be getting a new pre amp and using it's soundcard instead of having it on board.
Not sure if this is possible yet with the new bulldozer since specs haven't been released., dual xeons are way too pricey.
And yes, by slave pc i meant utilizing it's power, but I think this can be held off for a while with dual cpu in one computer.