We have 3 encoders involved in the audio import process (FLAC decode, OGG encode, AAC encode) and we can only support the features in common to all of them. Unfortunately since the AAC encoder is only a very simple one built in to Windows 7, we can only support 96 / 128 / 160 / 192 kbps, since the encoder doesn't support any other values. However, it looks like it's straightforward to add a downmix-to-mono option, so I'll see if I can add that.
If you need more advanced options beyond that, I would recommend finding your own encoders. We're not really looking to make C2 a super-advanced audio encoder program.Ashley2012-07-04 13:33:32