Very useful information there, DrLumen. Thanks for that.
It clarifies the disconnect between your expectations, and what we(including you) are seeing.
Among other things, when the rest of saw "previous versions", I don't think we were thinking quite that previous

.
I started with Sonar4, and the sliders then operated essentially as they do now. They are strictly audio controls.
However, the old Cakewalk line was mostly MIDI-centric, as I understand it. I have no direct experience with those products, and can only make my best guess based on what little I have seen mentioned of them.
Hopefully, some of the old guard will step in.
I suspect that the C5 sliders were reflecting MIDI CC or velocity data. It's possible they were audio levels, but the format in which the file is saved cannot be read by current versions. Since envelopes and their relation with the volume controls did not exist back then, it is most likely the necessary information is simply not there.
At any rate, I am fairly certain the console sliders will not behave as you are hoping for.
I think you may be in for a bit of an uphill run, but a change of tactics may be helpful.
Open the controller pane in your PRV. This will show velocity and other CC data embedded in the MIDI track(s). The PRV is a fairly powerful tool
Also, open the GUI's of the softsynths you are using. If they are responding to CC data, you will see the affected parameter knobs and dials move.
You may want to create volume envelopes in the synth audio tracks.
Do turn on the waveform preview in the synth audio tracks. It is very helpful for making adjustments in the volume envelopes.
Don't use simple instrument tracks. Just don't. They have their place, but not for what you are trying to do.
Another thought. Which softsynth(s)are you using? They all have various strengths and weaknesses
You are crossing a huge software generation gap. It may not be easy, but keep pounding away at it.
And don't be afraid to ask more questions. There are some pretty bright people here, willing to help.
Good luck.