I run CM300's > Nak MX-100 > UA-5 > JB3. Using the MX-100 in front of the UA-5 helps boost the signal a little bit and also that way I dont need to have the UA-5 gain knobs almost cranked. yeah, its more gear to carry (and the ole MX-100 is heavy), but it also helps w/ setting levels since the MX-100 knobs are a little more forgiving than the UA-5's are.
But to answer the original question, they do run kind of low, so the UA-5 levels need to be quite high. IMHO.
I love the Nak's for the price though.
Jim