Cactus Music
It appears to be for enhancing the listening experience of everything, Games, Movies and a lot of good stuff, but it was not designed with DAW recording in mind, nowhere is this mentioned in the user guide. It should work but to me it's like the negative experience I had with my Creative Audigy card which is in the same category as this one.   
It does not mention ASIO drivers anywhere in the manual, but I see from the OP's  list that it must use them. 
 
So I would say try a more reasonable sample rate even 44.1 and see what happens first. 
But the probability that the drivers are not going to play well with Sonar is high as we see all the time when people try using none trusted brand audio interfaces round here. Sonar is picky about drivers. 

I would agree with most of that except the last sentence. I find Sonar the least picky. 

Thanks for the replies.  To clarify one thing, as I said, I can see the green signal bar in the audio track moving (further to the right the louder it is) with each note I play.  Since this means Sonar is "hearing" (receiving) the sound ok from the sound card, then the problem can't be with the sound card, sampling rate, ASIO driver, or Windows sound input settings, right?  Otherwise, I would see no signal.  Or am I missing something (it wouldn't be the first time!).
 
The wav file gets created ok in the project folder, and there's no sound when I play it.  The other wav files and their clips that I recorded previously still sound ok.
 
Is it possible to see the input signal from the sound card, but it's garbled and so gibberish goes into the wav file, producing no sound?
 
In Control Panel -> Sounds, my default input is Line In, which is my sound card.
 
I don't see any 'output is assigned to silent output' message or other popup.  I still have it assigned to Xonar Essence STX ASIO(64) L. 
 
MusicJohnnie mentioned a possible routing problem in Sonar - how does that work, and is it possible to troubleshoot?
 
 
 
 
 
 
 
 

P.S. I tried it with sample rate 44.1, and there was no change.  The tracks I recorded successfully until now were at 192, and with the same ASIO driver.

In the Console View do you see the hardware outs? If you do are they showing a signal and are they going to the out on your sound card? 

Since you were previously able to record with this setup, what changed?

John - It took me a while to find the hardware outs, I'll look into it tomorrow.
 
abacab - nothing has changed that I know of.
 
 
 

If you are getting a wave file created in the project folder, can you play it with Windows Media Player and does it have sound (and the sound you expect?)

Hello,
Sorry for the delay. The routing troubles I was  referring to: somehow the audio signal was routed to the 'sends', and it took me awhile to find due to the fact that I disable the sends from module list to not show. I open them when I need them. Not often. Just a thought though, I haven't used it in a while. Could be your sound card is turned down on the output. Double check the settings on your output from your essence. Sounds like volume is off at some point. It looks like you have essence listed as 'L'. Is that for left side. Do you have a stereo out, or just left and right. Just thinking. There is an answer. Yours might be evasive for now. But, when you find the rascal it might be the...... 'DOH'....time.
Hopefully helpful
MJ

Dave - when I play the wav file that gets created, there's no sound.  The file is about the same size as other wav files that were already there (which I can hear) of the same time interval.  When I look at the binary in notepad, I can see the Unicode characters are very repetitive compared to the files I can hear (sort of like OOOO|OOOO over and over, but the chars are more exotic), so I guess it's filled with silence, so to speak.
 
musicjohnnie -my sound card has L, R, and stereo output, but I guess the output's not the problem, since the wav file is empty (nothing to output anyway).  I'm going to check out the modules/sends and hardware outs (as John suggested) later today. 
 
 
 
 
 

Sometimes in cases like this is imperative to start from the bottom and work your way up.
There are some very good replies here so I don't want to confuse you by adding more to the pot.
I will suggest however, you go back to basics.
- Check your Sonar preferences > devices.
- Make certain your devise is checked.
- Go to Windows Control panel and look for your soundcard in there.
- Make sure your soundcard is set up s the default.
 
If your using the same soundcard with other programs, gaming, You tube exc, Ive seen some strange things.
Those programs taking the soundcard hostage if you will.
 
Any serious work in Sonar should be done on a dedicated soundcard.
but im sure you've head that before so I will spare you the deet's.