Sander Mag Tech with Weiss 202 dac need help

Hi
Just got a Magtech amp, using a Weiss 202 Dac as pre,I have tried different out put setting just don't seem to be getting reasonable volume for the size of the room which is not that big 15ft x 12ft, if I use the highest setting 8.15 sounds stressed, if I go back to 4.15 find I to need turn volume near all the way up around 15 on the dial, to achive around 85db + peak, I had a Pass labs 350.5 before this, it was ok, should I be looking at get a Pre-amp and bias pass the dac, I don't need heaps of inputs only use Apple Mini, please help!