I suspect, what the software designer had in their shop was different to what the final release product was.. now playing catch-up due to the difference in internal hardware is likely the hurdle they have yet to overcome.

sometimes removing hardware to save weight and its functions in aid of half compiled software derivative may not always function the way it was intended to function a poorly designed tree likely doesn't help matter either..

it is more implementation than anything else which is the likely route cause of most of the issues with the UMC-1, until they address this I doubt it will be a true functioning piece of hardware until it gets addressed, until then it is a watch this space mentality with the UMC-1..

there likely a need for a proper volume tree which likely doesn't exist in its correct form.. I suspect all issues relate to eq and main vol and sub vol sets before and after you apply all the surround sound, bass management is only a subset of instructions, though is eq hasn't been dialed in correctly then no amount manual crossover hertage you use will never correctly set your mains, surrounds or subs, ref settings for thx will likely void any manual settings you configure..

you actually need a fully adjustable thx sub, having the perameters locked is likely causing most of the issues..