Welcome to the forum.
Are you wishing to Export as a stereo (2-channel) mix-down, or as a DD AC3 5.1 SS Audio stream?
For the former, the Export chosen should mix-down to stereo.
For the latter, you will need the Minnetonka Audio SurCode DD 5.1 SS plug-in for PrPro. If you choose the Export for the MPEG>AC3 DD 5.1 SS, you should get a screen, linking directly to Minnetonka's SurCode site. You will get a discount, as a PrPro user, from that link vs going directly to Minnetonka Audio and buying from that Web page. The discount was about US$ 50, but might have changed over time.
Let us know what you need, and someone will likely be able to direct you specifically.
The short answer is that Premniere Pro isn't capable of creating a 5.1 WAV file.
Now, if you just want 6-channel WAV (and DD AC3 5.1 SS is not an issue), just choose WMA, as the Export format. Export>AME>Windows Media, and the Windows Media Audio 9.2 Lossless w/ 5.1 48KHz should work fine. I use the WMA 6-channel for Export to Audition to structure my 6 discrete channels for conversion to DTS. Note: the WMA will NOT be DD AC3 5.1 SS, so cannot be used as a primary Audio stream in programs like Encore to author a DVD-Video, or BD.
Thanks for the reply but my intent is to create AC3 stream to burn BD without using SurCode. I am trying to follow the workflow described in http://forums.adobe.com/thread/511930 but not able to get the multi-channel output as described in the workflow.
I have modified my preference Edit > Preference > Audio > 5.1 Mixdown type to Front + Rear + LFE and default track format to 5.1 but still no luck.
When much cheaper priced Sony Vegas could do it but not Pr is beyond me.
Once again thanks a lot for all the feedback.
Sorry, but I use the Minnetonka Audio SurCode products to either create DD AC3 5.1 SS, or their DTS encoder. You will need to PM the author, and inquire about the exact workflow. The WMA 6-channel will get you the encapsulated discrete streams, but beyond that, I cannot help.
As for Sony's interaction with Dolby Labs, you will need to take that up with Dolby. I can tell you that Minnetonka Audio charges only slightly more, than Dolby charges them, for the SurCode licensing. All other business deals are beyond my knowledge. Remember, Adobe only offers a direct link to Minnetonka Audio, and they extend a "Premiere user discount." Minnetonka Audio holds the license from Dolby. If Dolby offers Sony a special deal, that is something totally different.
Good luck, and hope that you find the exact workflow needed. I thought so highly of the Minnetonka Audio plug-in, that I bought a license for both my laptop and for my workstation. I have never had a need to look beyond those. If WMA does not work, I cannot help, as I know nothing of that workflow.
I was fighting with the same problem 1 month ago with the same questions why PP is not able to handle 5.1 sound. After 3 weeks of lost life I understood that you need external software for processing 5.1 sound into AC3 files. Unfortunately compatibility of AC3 files is not easy cake. Maybe there is some free software able to make AC3 file accepted by Encore without transcoding, but I know about registered plug-ins only. I didn't like trap of Adobe/Minnetoka to purchase SurCode. Alternative option is codec from MainConcept. It is a question for you if it is easier for you to get MainConcept codec than SurCode. I already made 3 BD with AVCHD video and 5.1 AC3 and it is working. Unfortunately I am still not able to solve compatibility problem of M2TS video file between MainConcept and Encore. So, I am combining video from PP and audio from MainConcept in Encore.