From what I have read the iRacing telemetry allows wheel speed, tire temps, ride heights, throttle, Brake, Clutch, engine, gearbox, suspension, etc .. Now whether it is combined in one channel output I don't know, the sure way to find out is for you to read iRacings SDK which I believe is available.
You said you are not referring to console tactility, from my understanding you are only race with consoles, has this changed?, have you moved up to PC racing and if so which titles? You will find iRacing does not use any music at all, we are only dealing with race sounds, cars, track and wind etc..
I use the surround channel for my bass shakers because only inches away is a buttkicker on LFE channel, so a subtle difference was in order for me which is just a personal preference. Mclaren electronic systems offer telemetry which is pretty complicated from what I have read but I have not seen it personally yet as well as iSpeed.
As I mentioned, I have 3 zones for iRacing and each zone works just as I envisioned them too. Perhaps once you get going on PC racing, maybe even iRacing you can test these telemetry systems and come up with a well designed zoned layout. I would like to see your progress in this, but for now I have my tactile system working just as I want. I have invested a tidy sum to this point in my rig and I just want to enjoy this for now. Any other upgrades will have to wait for now.
Again for my sound system, I am totally satisfied with it, case and point. The Ford GT, the engine revs, the transmission, wheels squealing etc.. all at decibel levels that rival the real race car sound. I do not need a EQ to change any levels. I have a professional Tapco 2200 EQ which I could implement but it is not required. As far as I am concerned DTS Neo or DSP alternative modes mean nothing with bass shakers or buttkickers. I might at some point add 2 more bass shakers but to be honest 3 zones work good for me.
I know there are a lot of people that use the digital dash's, they are relatively cheap and easy to implement but I never have used them or even like them in either my real vehicles or my Sim rig. As I mentioned with them, they are only as good as the coder who designed them, some are better detailed then others, it's something you can research and decide which one suits you best. For the analog gauges we were limited by the rev burner design from Symproject and they have projects in the works that will include a burner for fuel, water, oil gauges and others. The next few months we should see advancements in that area. In fact if you join iRacing you will see real race car drivers who are also engineers who design all sorts of systems that are incredible.
I do appreciate you taking the time to write out a well though out detailed questions and comments Mr Latte. I am very much interested in seeing your tactile journey takes you and your design for your rig, if you have a link for your rigs progress I would like to follow along.