Hello Pat,
I am not sure how Classic set up the Hauptwerk audio settings for you prior to shipping your system, but my guess would be that if you are using multi-channel audio that each output is sent to the speakers as a mono channel, thus the recorded output will sound mono, but recorded as a stereo channel file (both left and right channels will contain the mono recordings, so they will appear as stereo according to any audio application, but will still sound mono since the left and right channels are duplicates of the same mono channel).
If you want a standard stereo recording with all channels mixed you can create an aux mixdown. See the tutorials page for how to accomplish this
www.hauptwerk.com/tutorials. Set the Recording output to none for all channels except for the mix down channels. When all other channels are routed to the mix down they will be recorded as a single stereo track. Then you should be able to convert to MP3 and upload the stereo file to the site.
If you are not using multi-channel audio then just check under General settings \ Audio outputs that the output channel format is set to stereo and that the Rank audio output routing settings when loading an order are also set to stereo and not mono.
If you need a specific question answered as to how your system was set up then I think that you would need to ask Darryl about that since he should know being the person who configured your system.