I guess I just find it hard to imagine what significant improvements can be made on the Revo 5.1, that's all. It even has a separate headphones output on the back - perfect for my requirements, down to the t.
The very lean and non-resource-hungry control panel also gets my vote - something that can't be said for the old Audigy drivers that I used to have for the Audigy 2 Plat.
PS. Revo 5.1 is reputed to have a better DAC for all 5.1 channels than the 7.1, which uses a good DAC for the front 2 channels, and uses an inferior DAC for the remaining 5.1 channels.