Although current DVD recorders cannot record in 5.1 channel Dolby Digital or DTS audio, when used with an AV receiver equipped with Dolby Prologic II and/or DTS neo:6 processors, the two channel audio recording can be reprocessed into a 5.1 or 6.1 channel soundfield, albeit not as accurate as an original 5.1 or 6.1 channel Dolby Digital or DTS soundtrack source.
The reason for this is two-fold: Since you can't record (or shouldn't be able to) or copy DVDs and there is little 5.1 or 6.1 channel audio available from other sources to record, there is not much need for this function (although this is changing as more cable and satellite programming is transmitted in dolby digital 5.1).
However, the second factor is probably more political than technical: even if you are successful at making a copy of a DVD video, you are prevented from making a copy of the multi-channel soundtrack, thus preventing you from making an "exact" copy of a DVD on a DVD recorder that could be "passed off" as the original.
Lastly, it must be pointed out that there have been indications by a couple of manufacturers regarding the possible introduction of DVD recorders with 5.1 channel Dolby Digital recording capability, but none have actually hit store shelves.
On a side note, Sony has released some camcorders with with 5.1 channel Dolby Digital recording - hopefully, this will filter into DVD recorders.
If the status of digital audio recording changes for DVD Recorders, I will post an update on this question.
