no need to set the recording (input) "volume" of the pmd670.. feed the marantz a digital signal from the v3 and set the pmd671 to "digital in"
mic into v3's xlr inputs > spdif digital out > digital cable > digital spdif into pmd670
then control the input via the knobs on the v3.. turn them up untill you get levels peaking near zero on the v3.. if it clips (peak reset), ease back a bit..
also.. set the v3 to 44.1 and hit the little "ansr" button so it lights up.. (or 48 if ya want)
OR
if you are running analog out of the v3 to the 670, I would imagine you would have to set the input level of the 670.. I cant help you there as I dont own one..
hope this helps!