When you say, "they have asked me if I can get them some recorded material" you mean, they'd like a recording of someone singing a song with a backing track or whatever is coming out of your mixer?
If so, that's cake.
On the back of the DFX-6 are two RCA jacks labeled 'Tape Out'.. this is the same signal as the 'Main Out' that you feed to your speakers, except it's at what they call 'line level' in volume.
I regularly record some of my better singers at shows to upload to my website, or even play in between singers on slow nights.
To record on your laptop, you can use the FREE Audacity software available here:
http://audacity.sourceforge.net/
There ought to be some kind of Mic input on your external SoundBlaster device.. if not, score a Behringer U-CONTROL UCA202 USB-Audio Interface.. they work great, sound great, and Musicians Friend sells 'em for $30!
Musicians Friend link
Just use a set of common stereo RCA patch cables to go direct from your mixers TAPE OUT to the INPUT of the UCA202 and record away!