dmm

I am having an issue, I was able to set my subwoofer amp gains to the calculated 50v fine (nvx xad13) (sounds and works great), I go to set the gain on my sundown sdx 200.2 and gain maxed at the same volume I set my sub amp (same volume on the same headunit I had my last setup running on fine)...

Will a cheap (ebay-bought) DMM work for setting my gains? I don't want to spring for an expensive one since this is all it will be used for. Thanks.