I'm currently using SONAR Platinum and Creative Labs Sound Blaster Z.  I'm getting latency which is tolerable with slow songs; however, with faster tempos the latency presents a challenge.
 
Is there another (better) soundcard I could try that would get me closer to the holy grail of 'zero-latency'?

There are tons. Look at Focusrite, RME, Tasam and so on. You want something Prosumer or better.
 
Regards,
Dan

I have a Focusrite Scarlett 6i6.  I've been using the Creative Labs Sound Blaster Z because I can't get it to work.  Any ideas?

An idea I mentioned here:

http://forum.cakewalk.com/Hardware-f82.aspx

Hi. Do you have the latest ASiO drivers for your 6i6? Make sure you are not connecting via USB3 port, and do not use a hub when connecting your 6i6. What issues do you have with your 6i6?
All the best.

And for recommending another Interface, I can only say good things about RME.
 

Oops!  I had it connected through a USB3 port.
 
Where can I download the latest ASIO drivers for the 6i6?
 
What are the following SONAR Platinum settings:
MIDI > Devices > Inputs/Outputs
Audio > Devices > Input/Output Drivers
Audio > Driver Settings

You can download from focusrite.com. (You may have to log in) You use your 6i6 for everything. Take a look in the manual, both 6i6 and SONAR.
All the best.

Thanks!  I have not downloaded the latest drivers yet; however,  it is working!
 
Question(s)
1. Scarlett MixControl have to ran first before running SONAR Platinum?
2. What is the optimum ASIO Buffer Size in Scarlett MixControl?
3. How do I get the volume output I had with the Creative Labs Sound Blaster Z?  (Seems a little low)
 
Thanks

I do not own a 6i6, but I believe that MixControl will start with Windows, if not stated otherwise. Try to keep it as low as you can without getting dropouts. This will be different from system to system. Keep it around 10 ms, or less (if you can) when recording. You can up the buffer when mixing. Check the manual and MixControl for volume.
All the best.