Cubase Pro 9/UAD-2: Can't render group tracks. Please advice.

I am working on a remix of an old 80’s album and all tracks from the original 16 channel tapes are stored as mono wavs. Some of the tracks are actually stereo pairs, e.g. tom mix, over heads and some synths. be able to treat these track as stereo tracks I have paired them using group tracks.

The problem now is that I need to reder some of these group tracks to save up DSP power, but it seems like you can’t render group tracks in Cubase or am I doing something wrong? Or is the a work around?

Otherwise it would be interesting to learn if there is any easy way to create a stereo track from two mono tracks.

Thanks in advance.