Preamp for zen 4 (would this work ?)

Im thinking of building this preamp for my zen penultimate.
http://sound.westhost.com/project37.htm

My question is simple

would there be any problem using it ?
i mean is the impedance a problem for the zen ?

At the moment im running straght from my computers soundcard to the zen ..however the lack of volume is disaapointing ..
Removing part of the feedback circuit certainly increased the volume ..but i know thats the wrong thing to do LOL

Bias at 1.5 amp is great but
With Bias around 2.6 amp ..bass is much more deeper and overall sound is ..how can i put it ........closer