Wave 0/1
This device can be used for multichannel playback (such as Sonar, DirectSound 3-D and DVD applications). However, due to multichannel support, it requires slightly more processor power and, thus, it is not recommended for latency-critical applications, such as Sonar (but 10ms latency can be easily achieved). Note that most applications that open the 'Wave 0/1' device in 'stereo' or 'mono' mode are not affected by software processing because it is automatically turned off.
The output of this device is routed to 'Generic Stereo' signal path and it gets mixed with Synthesizer output as well as 'front' outputs of the Surround Effects (Reverb and Chorus). It is up to the 'Surrounder' effect to choose, where the 'Generic Stereo' signal gets routed to. That is, it can be panned* between 'front' and 'rear' speakers (* this feature is not supported at the moment).
Wave 4/5, Wave 6/7, Wave 8/9
These devices route directly to your hardware outputs. Wave 4/5 is routed to 'front', Wave 6/7 - to 'rear', Wave 8/9 - to 'center+subwoofer'.
The Wave 6/7 output additionally gets mixed with 'rear' outputs of the Surround Effects (Reverb and Chorus). If you wish to use kX Audio Driver for '5.1' playback (DVD, Games), use the default connections (don't forget to swap 'front' and 'rear' speakers). Otherwise, you get 3 independent stereo outputs that can be used separately. Also note, that 'Wave 4/5', 'Wave 6/7' and 'Wave 8/9' do not require additional software processing (compared to 'Wave 0/1') and can result better latency under Sonar and similar applications which use 'Kernel Streaming'.