When X1 came out I tried it with my old Audigy card as well to see if it would work. Sadly whatever I did... there was no dice.

I wasted a few years fighting with a creative Audigy II and trying to record with Guitar Studio and later Sonar 7 Pro. It worked no problem with Wave Lab. The MIDI never worked. 
And later what I found was that each track I recorded was out of sync, I did some tests. So you are welcome to waste your time trying to get it to work like many other Sonar users who have done the same. It's your time. 
Sonar needs a proper audio interface , end of story. 

Before I got a better card, I had no trouble using a sb audigy but with kxproject drivers... Good luck!

kx project drivers were for windows XP 32 bit. And they didn't help me at all. They gave you the option of multiple outputs which was cool. But the sync was still out when multi tracking. 

I have the solution for you. open your PC up so you can see the soundblaster card. Then take both of your hands and rip that piece of crip out of your PC. Wait!!! i'm not done. You have to make sure the SB card can never be used again. So take that SB card and go to the highest building in your city and drop it form the roof. Then after that, take all the pieces that are on the ground and pour lighter fluid on them and proceed to light every single piece on fire,. no piece is too small. Its like the Terminator. Yuo must make sure its DEAD!!!
 
OK, I think that will do it
 
CJ

Yup, alien technology...

not sure if its been said but if you have a wireless card for internet, disable it in device manager.
I had this problem once on a laptop. it was mind boggling where the noise was coming from until I figured it out
(with help from Beagle I might add)

Hey CJ,, where I live the buildings are only 3 stories high,, do you have another solution? 
 
- my son gave me an old PC a few years back and it had a Audigy I card --you've never seen a screwdriver works so fast!!` , so I have a Audigy II and a Audigy I sitting on a shelf now.. 
I should put them on E bay and offer money to anyone who will take them away which will save me a trip to the city to find the building CJ is saying I need. 

DavidWilliam
However, the problem that I AM having is that I keep getting a crackling sound during playback.  It comes and goes, but it's there.  Anyone know what might be causing that?  (I know the obvious answer is, "Your cheap sound card is causing it," and maybe that's true, but I've ALWAYS used cheap SB cards, and never had any crackling before.  In the past, I worked with Sonar 4 and Sonar 6.  This is my first time using X3, so I'm wondering if maybe there's some difference I'm not aware of in terms of settings.) 

Cheap as it may be it should still work. Be sure to run the Wave Profiler, then play with the Mixing Latency settings. Start with full Safe and work back one notch at a time. There were times when I could only find one specific spot that would stop the krispy kids from playing with my SB card.
 
As for the OP's hum issue, I had the same trouble when using an analog mixer with SB cards. I don't remember if I ever found a solution but eventually I bought a USB interface and have never had hum since.

johnnyV
Hey CJ,, where I live the buildings are only 3 stories high,, do you have another solution? 
 
- my son gave me an old PC a few years back and it had a Audigy I card --you've never seen a screwdriver works so fast!!` , so I have a Audigy II and a Audigy I sitting on a shelf now.. 
I should put them on E bay and offer money to anyone who will take them away which will save me a trip to the city to find the building CJ is saying I need. 

Do you have a car or access to one? If you place the SB card on the street and drive over it repeatedly as needed until there are only little pieces left. Take them to the nearest environmentally safe incinerator and incinerate them. Be sure to take the ashes and pour hydrochloric acid on the ashes then neutralize with a base and goto a far off land fill dig a hole deep in the middle and place the neutralized ashes in the very bottom of the hole and then fill the hole with concrete and topped with a warning sign reading "hazard" Sound blaster remains buried here not fit for human contact for 1000 years. While you're at it do the same to any iPods and ear buds you have.