Well the good news is, you have multiple stems to play with. Having your stereo mic’d room pair plus the SBD means you’ve got a better chance of getting the end product you want.
I would suggest you first consider and concretely define what it is you want to accomplish. I can’t tell you what sounds best, only you can. And I can’t tell you what the “right” way to do something is, either - how much adjustment to make to levels, plug-ins, etc. I further could not tell you what the preferred workload is. All I, or any of us, can suggest is what works best for us. To wit, I encourage you to experiment with as many techniques as possible til you are happy.
What I CAN suggest, is insight into what works for me w/r/t the process at large.
Generally, the question I ask is “what did I think the music sounded like in the moment, and given all recordings I have on hand what is the best way for me to let my recording get out of the way between me and enjoying the music?”
Do you think the aud generally sounds great, but wish you could add a touch of definition or clarity? That’s where Kyle’s method *shines* - get your room pair generally sounding balanced to taste, then use the SBD at very low levels (I generally set the SBD 20-30 dB below my mains pairs when I do this).
It’s worth identifying the distinction between what I will call the “dry” mono sound board and your stereo AUD mics. Your AUD has something the sound board does not - a room. Reflections massively influence your perception of a space, and those reflections do a lot of things to help you localize a mono sound source. Your mono SBD is being pumped through a set of filters - an amplifier, then a speaker, then the greater room impacts. Most of those can be generally compensated (the amp + speaker), but a room is a different beast that’s crazy hard to model. This was actually the origins of reverb algorithms in the mid-late 70s: David Griesinger was a recording engineer and had stereo mains of a piano/violin/cello trio, as well as close mics of all 3. He loved the mains but didn’t hear enough cello; so he went to add the close mic cello, but it didn’t blend with the other instruments in the mains - it was too immediate and direct. He also happened to be incredibly intelligent and the senior engineer at a company called Lexicon, so he researched and created the first concert hall algorithms in DSP. All this to say, Gutbucket’s suggestion of adding a room reverb to the mono sound board is a great way to “stereoize/spatialize” a dry mono SBD recording, especially one with so few musical elements likely played in dual mono over two PAs in a room. If you configure the reverb algorithm right (“size” and “decay” controls), you should be able to get both pretty close.
If you think the SBD sounds great but could use more “immersion” or “space” - the mythical realism of being in the crowd - you could set the dry mono SBD board on its own, and then slowly and quietly bring up the AUD underneath it until the blend sounds good. This is treating the AUD as your “reverberation algorithm”, and if you can get the blend of wet/dry right you can find some good results there too.
iZotope can be a magical tool, but I find it generally ends up being used to polish a less than stellar recording. I’ve heard a lot of tapers here use it to great effect, and I come from a studio production world where it does wonders for restoration work especially, but the DSP engineer in me cries every time I think about what iZotope does to the phase response of any recording. This to say, it’s not a tool I find comfortable or intuitive to use for my own work, but that’s not a commentary on if it’s a good tool or if it’s the right tool for you.
Avoid a binaural audio planner. All it’ll do is induce a head related transfer function, which artificially adds ITDs/ILDs (directional cues based on interaural time and level differences) that don’t exist in the recording and cannot be undone losslessly. And additionally, it adds those cues on top of your headphones or stereo, which themselves induce even more cues for your brain. I’d also avoid any ambisonic encoders, on a mono source it’s just fancifying mid-side encoding that will permanently distort your phase response.
To the meta-commentary on trying to clean up a recording in general… I’ll comment that this is why the most important microphone in my locker is my hypercardioids. I don’t love how they sound, and while I can enjoy recordings made with them I find myself not loving them the way I do my other microphones. But the hypers are a tool - if I’m in a chatty crowd, or a less than ideal location, I know they’ll always make a listenable recording with minimal possible wookery, and if I deploy them right I can do away with “room boom” in the bass and “haze” that too strong of reflections from the back of a hockey rink will bring me. I think my cardioids make much better recordings in general that I consistently truly love, and my subcards in the right spot sound sublime. But I reach for my hypers first, they’re what I prioritize running if I can only have one pair in a compromised spot, and I am always happy I have *a* clean recording when my other mics turn out too chatty. All this to say, I encourage you to prioritize grabbing a pair of hypers.
Addendum edit: it is crucial you get all your recordings time aligned if you’re going to mix them down. You will be in phase hell if you do not. And if that’s too much work, it might be worthwhile just to post the sbd and aud as individual releases, allowing your listeners to choose which recording they’d rather hear - it prevents any permanent phase destruction in either recording.