You can use analog out for 7.1 audio from DX/D2X. Problem with them is that they cannot pass true HD audio by bitstreaming (through HDMI - 5.1 is maximum that is supported by spdif because of bandwidth limitations) so that and external AVR/amplifier like onkyo 606, denon 1909 amongst other can process it.
What the Dx/D2X will do (actually the software like MPC or Cyberlink power DVD decodes the true HD audio to analog streams in 7.1 format which the d2x/Dx deliver) pass 7.1 analog audio - you need a receiver with analog in (7.1) for that. Most budget receivers do not have that and hence you have to stick with computer speakers.
Xonar HDAV 1.3 (highly overpriced for a feature that the HiFi and movie industry overlooked during their thinking process) can pass 8 channel audio via bitstream untouched (so that software doe snot decode it and create problems) to an external receiver which can then use it HW to process the audio. Thats it man.