Hrm. It's been quite some time since I had to work on this issue; I believe this MSDN article may have some pointers:
There's two different ODBC Data Source clients in 64-bit Windows systems, it seems; if you're using the wrong one, you may not be seeing the Access client in the Connection Pooling tab.
Ulitmately, though, I don't believe connection pooling fixed the issue I was having back then; it stemmed from the network configuration at the time. We had a router, plugged into a switch, plugged into a bunch of computers and a switch, and that switch went to a bunch of computers and another switch, which went... Yep. It wasn't pretty 😛
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