You’re using c-ducers for the piano plus two contact mics and these open and close the gate on the shure? Then you add 2 mics for air? Live you use an audio bass end, but is this the only mic?

I think you’ve totally misunderstood how pianos, especially grand pianos work. Forgive me if you’re a mega expert. First thing is that make matters. For instance, a mic under slung from the bracing facing up works on a Yamaha C3 and G2 works very well. Terrible on others I’ve tried, including other Yamahas.

what sort of music is it? That’s very important. Do this test. Find a condenser you trust, and a sealed pair of headphones and while your music is being played, move it around. You will find that the bass strings are not making the noises you expect. The bass tone is a product of the contribution the entire sound board makes. A mic on the treble side picks up a lot of bass. The other very critical thing is that you’re  overdoing it. I have never had the need for more than two mics. You’re up to what, five channels? That’s crazy, they’ll never balance into a grand piano sound. Maybe what you’re trying to do is get separation of the bass strings? That I get, but close miking the bass strings sounds horrible. The classic two mic technique most people call stereo isnt stereo at all. Both have soundboard plus separated mechanical noises and the string clicks. My Yamaha grand I now own, I bought from the hire company I got it from for live shows. On stage, depending on the event, it would be one mic, probably an AKG 451/CK1, or for piano centred stuff, two 414s. Plenty of gain before feedback, but if I wanted bass heavy stuff from it, it would have howled like crazy. I’ve never owned c-ducers, but they’d be more gain before feedback capable. Having recorded and done live grand piano recording for a long time, you’d be surprised how little adjustments in position do to the sound, apart from highlighting, or reducing things like the hammer impact, the damper thumps and releases and the noise of the keyboard mechanism sliding sideways with pedal action. Moving the mics changes this stuff but rarely changes the actual sound very much at all. For recordings I might put the two contacts taped to the underneath of the lid on full stick. That can be nice. Live, I did a German demonstrator doing a classical concert for Yamaha. Nice guy but he beat the heck out of the piano doing Schubert. I was pondering where to mic it up and he came over and said, on zis piano, you vil get ze best result here, vatch. He took the 451 in my hand crawled underneath and hug it over and down from a strut about a foot away from the pedal board frame, he then bent the cable back up and taped the mic to the up and down mic cable, about a foot beneath the soundboard, facing up. It worked amazingly. Everything I’d been told about never doing this went out the window, but he warned me only some pianos are going to work, and absolutely NOT Steinway. 
 

I suppose using a short full size keyboard at the side for your left hand is out? That would give you access to different bass. No idea what your genre is. My guess is that maybe filtering off the left hand, then processing just that as a separate source might work? 
 

all this rambling is guess work without hearing what you’ve already tried and are not happy with.

if you play live, do you have to use random grands in the venues?