No updates on the problem itself from Penteo unfortunately, but having listened to JRSS upmixer, in combination with the Dolby Access Upmixer (recently introduced on the Dolby Access app under settings), I've observed the following, relevant to a 7.2.4 surround setup:
1) JRSS Upmixer + Dolby Access Upmixer works best WITHOUT Volume levelling or Adaptive volume enabled.
2) Set subwoofer to Silent - allow your a/v amp to do the bass management. This WILL make things sound less powerful, and so that's when you need to adjust your sub back to a level where it's comfortable. I found that this then put my sub in parity with the rest of my system when not listening through Media Centre.
3) Make sure your sub is properly dialled in to your speakers at a crossover that suits your listening environment. If it isn't, it creates some very strange effects.
4) Room Treatment and modes / antimodes.
Make sure your room is treated to remove standing waves /peaks / nulls and / or you have a DSP which flattens the peaks properly.
I've glued some rather thick acoustic panelling to the corners of my home office and some other panels to larger exposed wall and ceiling surfaces. I also use a DSpeaker Antimode in combination with this. The acoustic panels tamed the sub hugely, but note that if you're disappointed after DSP sub calibration through an antimode device, just increase the gain on the device for the sub. It's that simple.
5) Dual subwoofers.
Now, I've read all the threads about "summed bass response" and through practical tests now believe it to be a flawed process. Each sub has their own correction curve. Period. I don't care about the physics of this, I can only tell you what I've discovered.
My a/v amp has 2 sub outputs, and the DSpeaker Antimode Dual Core has 2 sub inputs. This allows each one to be independently dialled in by the Antimode, and then summed through its algorithm to deliver a far superior result both in immediate response AND decay times.
Summed bass response for me left a massive gaping hole between 60 and 100Hz, with a -27db dip at the worst points, which did NOT correct during decay.
6) If you're on Windows 10, make sure you're running the latest Dolby Access app, and you'll find the upmixer in its settings. You need to enable 5.1 / 7.1 audio in your Windows audio settings and then turn on the upmixer. Your a/v amp will then register the PC's outgoing audio stream as Atmos, and you WILL hear your overhead speakers kick in.
7) Once you've done all that, now you can turn on jriver's jrss upmixer, and check it out. You'll need to pump the volume up a little higher than you're used to, and as mentioned above, allow your bass management to occur through the amp, so set sub to silent.
This will give you the absolute best quality from the JRSS upsampler on Win10. Some people say they don't like the phasing, some that they can't stand the thinness. I believe these are psychoacoustic effects which are the result of listening to multiple channel bass reinforcement, for example, for so long using the other techniques.
So now I find I can switch between the JRSS upmixer and the Clone Side Channels to Rear Speakers options without hearing weakness in either setting. They're DIFFERENT, but one is not intrinsically weak compared to the other.
Again, from a subjective standpoint I can only say that whereas the JRSS upmixer attempts to place you a little way from the orchestra, filling the front soundstage but also allowing atmospherics to appear around you to grant a sense of immersion, the Clone Side Channels To Rear Speakers option places you on stage, in the middle of the orchestra, and is the closest in-room experience you'll have to wearing headphones.
What I was originally looking for with Penteo was something that achieved a more detailed and nuanced version of the Clone option, but now what I realise is that it's BECAUSE channels are cloned and allowed to interact psychoacoustically with the listener that creates the soundstage in the middle of your head as headphones do, but without the physical encumbrance.
I hope this guide is helpful to someone.
Best,
Marc