"i have an audigy as well working at the same time"
I strongly recomend to disable/uninstall the audigy and re-install drivers for your audiophile 2496. Try to download the latest drivers from m-audio.
In the other hand, Sonar does work with ASIO drivers from version 3 and up, if i´m not wrong. Try to configure Sonar to use ASIO drivers with your card instead of DX or MMC drivers. They give you best performance, less latency.
The volume issue maybe the playback resolution is set for 24 bits, and when listening to 16 bits audio files, sounds quieter than it should. This can be corrected in the Audio Options in Sonar as well.