thanks for the reply..
for myself..
1.) can 'dual' output be done on an UNO/Duemilanove? (I though I had read only on Mega's? could be wrong of course.. I thought i had 'tried' it originally and dont recall seeing (hearing) a difference.. however that could also have been user/set-up error.. LOL
also.. as to the noise I guess I was referring to.. I mean more specifically wen you run/do PWM actions 'while' playing audio.. you can hear the hum/buzz..etc..etc playing over the audio or interfering...etc..
unfortunately.. I dont have any 74AC14 chip.. (never even heard of them before now) :)..
but I do have a LM386 amp laying around..?
form the schematic though.. looks like only a:
coupling cap on the power rails
2 x resistors..
and the DC blocking cap on the PIN9 output?
actually looking again.. is that two caps for the decoupling? hard to see in the fritzing image) 
Are you saying that just using the DUAL PWM output will (not only help eliminate the noise) but increase the volume.. to where you say/think/believe no amp is even needed to boost volume?
I currently only have things set-up for single (pin9) output.. and actually used pin10 as the CS pin for my SD card..
but next revision could have that changed easy enough......
I'll have to go back and try the dual output again?
thanks.