DG gave you an interesting alternative that i was not aware. It seems that a couple other products could help you as well.
The actual tendency for large projects is to run heavy plugins or instruments on a remote machine, sending MIDI, AUDIO and automation (and even VST plugins code) through a low cost gigabit Ethernet link to another computer running a server software executing the plugins remotely. Then on the local computer, you load a client VST plugin connecting to the remote server so that the local plugin code can be sent and executed on the remote side.
There is no more reasons today to use expensive DSP hardware when a single multi core Intel processor can give you more processing power and a lot more RAM than the biggest DSP card available.
A well known product is “FX Teleport”, sadly the company is not anymore in activity but i’m sure there are other products available or that will be available shortly. FX Teleport is still available for download with a free license even if the company is dead. Nevertheless it’s certainly only 32 bits and perhaps not tested with recent setups.
I’ve notified as well in the same area a product named “AudioPort Universal” that could help you as well.
The goal is to eliminate costly (and not always reliable because of bad drivers or digital sync problems) audio cards and keep the system open and extensible just adding remote computers linked by a very fast and reliable well tested interface (gigabit Ethernet).
Another great advantage of using Ethernet, is that it is a very standardized solution where you can use switches and low cost cables with up to 100 meters distance between each device, so that you can extend your setup in a very efficient and low cost way compared to the traditional digital audio cabling system.
Ethernet latency at 1 Gps is very low (< 1 ms) so for audio applications there is no concern with latency and anyway it can be fully corrected during mixing jobs.
Hopefully the next version of Windows will have a system driver for linking audio and midi through Ethernet.