I don't know any advantage to sending stereo samples to mono speaker channels instead of preserving stereo all the way through, but maybe I've been missing something. In any case, adding IR to stereo buses works fine.
The simplest approach is to mix down all 7 source stereo pairs to one master bus and add reverb to the master bus, then output that to your reverb speaker pair.
It's possibly better to add reverb to each source stereo pair so the sample and its reverb sounds from the same speaker pair. This is like a wet stereo sampleset like Metz or Salisbury.
I like sending each source stereo pair to a different intermediate bus to add individual reverbs to each stereo pair, in order to send the reverb to a different pair of speakers for each source (limited to 8 intermediate buses). It's like a surround sampleset with multiple stereo pairs in both the front and rear audio groups that way, instead of ganging all the reverb in one pair of reverb speakers or having the reverb come from the same speakers as the source signal. That's a bit more work to set up, but I like the results best in my audio system.