Sanderxpander
I had lots of problems with midi when I had ASIO4ALL installed, even when I wasn't using it. If that is anywhere on your system at all, get rid of it before doing anything else! 

Preach it, brother. Probably doesn't relate to his issues, and tends to be very system specific, but it's worth mentioning periodically to warn others.

jtmusicAnalog
...do I have the patience for a DAW that craps out straight out of the box and takes lots of effort and help and posts to resolve, whereas other DAWs are generally good-to-go from the get-go.

The reason this might seem like such a wild goose chase is precisely because SONAR, like all DAWs, is "generally good-to-go from the get-go". So, with no precedent to reference, all the questions and suggestions are inevitably 'shots in the dark'.
 
The symptoms you're experiencing are very unusual, to the point that I would tend to suspect there's some basic interoperability issue with the hardware platform or operating system configuration.
 
Have you by any chance tweaked the Windows Performance setting to give priority to 'Background Services'?

OK, folks, I'm back. Thanks again for all the helpful posts.
Had to step out for a bit and haven't gotten around to installing anything yet.
No, I do not have ASIO4ALL installed, so, safe on that end....
My Windows 10 Prof. x64 is set to "High Performance" in that setting; I did not find where to change a setting to give priority to background services....
 
Think I'll take the advice of installing Sonar Platinum through Control Center first, and see where I get with that.....
I'll be back....

Hey folks!
Well, I installed Sonar Platinum K.... (Demo), a "clean" install.
Loaded the stuff from the tracks I was using, assigned the same VSTi stuff as before and...
This time, I didn't get any issues or stuck notes as per before. Note that I used the ASUS Xonar as the audio interface, the Tascam device was disconnected, and no Controller keyboard was turned on.  So, obviously I think, there is some setting somewhere that wreaked havoc on me, and not necessarily the hardware. I think before I progress any further, I will connect the Tascam device, and see what happens with the playback (and Stopping.) Then power up the Oxygen Controller, and see how that behaves.
 
What do you all suggest I try next?
I'm thinking, uninstall Sonar Plat. (through Control Center), clean up after it, and install Sonar X3(e). If that works now, then I should be good to go on X3, and not have the need to purchase the latest Sonar. If X3 gives me troubles, then I'd need to revisit purchasing Sonar Plat., as I know now that supposedly can work....
Will keep you posted....

OK - no issues with the Tascam interface or the Oxygen controller. Safe to conclude those aren't the issues.....??
Going to remove Sonar Plat., and give X3e a shot.....

Finally!!! X3 is working on this song fine now!!!!
I guess some setting somewhere was incorrect, or causing the problem, and re-installing and re-initializing Sonar and the Aud.ini file did the trick!
Yay!!!!
Thanks guys!

As the I Ching says, "perseverence furthers." 
 
Props for not coming in here, saying we're all idiots and SONAR sucks, but instead trying the suggestions and achieving a resolution. Not everyone does that...!
 
 

I think still to move further... SPLAT. [It has worked till X3], but JTMusic have to get this working on SPLAT.
Am I wrong?

Snehankur
I think still to move further... SPLAT. [It has worked till X3], but JTMusic have to get this working on SPLAT.
Am I wrong?

I'm pretty sure his goal was to get X3 working. In post #44 he said Platinum was working. I think Platinum is a better product, but X3 works well, and he might not want to spend the money on a new program.

agreed, Mr. Anderton. I'd only buy Sonar Plat. if I absolutely had to...
A big thanks to all you folks for your posts and help. It was all your generosity and insistence that things could be fixed that drove me to keep fighting and give all this another chance. I'm glad I did!