Thanks, Bob!
I tried your suggestion, and it worked-- I was able to playback the music without any crackling, crashing, etc. 
Now, this may be a stupid question, but if I need to raise the ASIO buffer for playback, wouldn't I also need to keep it raised when I'm recording?  For example, say I recorded 9 tracks worth of music, and now I want to overlay the 10th track.  When I'm recording that 10th track, I need to be able to hear the other 9 tracks while I'm recording.  But if I lower the buffer, I'll get the crackling/popping/etc from those 9 recorded tracks.  On the other hand, if I keep the buffer raised, I can't record properly because of the latency.  The only solution I can think of for such a case is to lower the buffer, freeze all the tracks that are just playing back, and then I should be able to record the new track, but that seems extremely tedious.  Are there any better workarounds?
 
Also, stupid question #2:  You mentioned a "dedicated audio interface."  My understanding is that an audio interface basically just gives me extra inputs, etc. (which I don't need, since I'm only using softsynths.)  But, based on your suggestion, it seems an audio interface may actually work as a sound card.  Is that right?  If I were to buy an audio interface, could I use it INSTEAD of my Sound Blaster?  If so, is there a particular audio interface you recommend for someone like me who really doesn't need extra inputs and simply wants something that will play back my music more efficiently?
 
Thanks again!

You don't have to use the lowest setting. Four ms latency is great but if you used say 10 ms instead, you probably would not hear the delay and your processor probably wouldn't protest as much.

The problem has been solved!
 
First step, I optimized Windows 10 for audio by shutting down some unnecessary apps that I didn't even know were running, and set my computer to high performance mode.  I basically just followed these three steps that I found at another site:
1. Set my computer's power for high performance
- Go to: Control Panel>Power Options
- Choose "High Performance"
- Then click the "Change plan settings" button. Make sure both power options are set to "Never".
2. Disabled system sounds
- Go to control panel and select "Sound"
- Go to the sounds tab
- Under sounds scheme, select "No sounds"
- Click "Apply" then, "OK"
3. Set processor scheduling to "Background services"
- In control panel select "system"
- Go to "Advanced system settings" and then the "Advanced" tab
- Click on "Settings.." under Performance to bring up the "Performance Options" window.
- Go to the "Advanced" tab and set processor scheduling as "Background Services"
- Click "Apply" then "OK"
 
 
Next, I followed Greg's advice above, and set the latency to 10ms. 
 
Then I opened a project that had been particularly problematic, played it, and did not hear even one crackle during playback.  Everything went smoothly.  Thanks for your help, guys!