Hexy-
The analog dbu measurement that the MP2 lights indicate is different from the digital db (or more correctly dbFS -- decibels Full Scale) that is indicated on your A-D converter or your recorder.
Nobody here will be able to tell you where to have the levels set according to the dbu scale of the MP2 as it will depend on the design specifics of your A-D converter (or recorder if you are using its internal A-D), which we don't know. In general, the relationship between the dbu LEDs of the MP2 and the dbFS of your A-D will not be that readily understood, so you will be much better off setting your levels according to the A-D converter or recorder than you will be using the MP2's meters. (And as you probably know, when setting against digital dbFS meters, you want to get as close to 0dbFS without going over as you can, though you might want to back it off a bit to give yourself some headroom.)
If you don't have the greatest meters on your A-D converter and/or your recorder, you can try to get a feel for where the levels should be according to the MP2 meters, but this will probably be a trial and error thing. Unless you know what the input level requirements are for your A-D converter. For instance, if I recall correctly, the V3 requires a 28 dbu signal level in order to meet 0dbFS when the V3 is set to provide 0db of gain. So if you used a V3 and had the gain set to 15db, you would need to send a signal of no more than (but approaching) 13 dbu, which you could read off your MP2. This info on the relationship of input strength (measured in dbu) to gain level and digital decibel level Full Scale may not be published for various recorders and A-D converters, so as I said, you're probably better off either using the meters on your A-D converter, or just doing some trial and error with your set-up to determine what gain level of the MP2 seems appropriate.
-Todd
Edit: sorry, I didn't see before that the MP2 would be run with an SBM1. Everything else above probably still stands, since I don't think sony has published the input requirements for the input signal strength level needed to reach 0dbFS, so you still won't know how much gain to run according to the MP2 level meters other than trial and error.