For the ASIO driver problem, you'll need a 64-bit ASIO driver if you're using the 64-bit version of Mixxx. Otherwise, I *think* using the 32-bit version of Mixxx with a 32-bit ASIO driver will also work on a 64-bit OS.
For the ASIO driver problem, you'll need a 64-bit ASIO driver if you're using the 64-bit version of Mixxx. Otherwise, I *think* using the 32-bit version of Mixxx with a 32-bit ASIO driver will also work on a 64-bit OS.