Very Computer

I am in the market for a Socket 478 motherboard that supports Hyper Threading.  
Can anyone recommend model that does not include an onboard video or sound.

You might check Supermicro.
Possibly the X5DA series.

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Those are dual socket 604 boards---a long way from the single 478 the OP
wants.  (All SuperMicro "X5" series boards are socket 604 Xeon
boards...some single, most dual CPU.)  Something in SuperMicro's "P4"
line might be more suitable for the OP, perhaps the P4SBP even though it
has onboard audio (which can be disabled).