internal clipping Marantz PMD-670

I'm using the PMD670 for field recordings, i.e. on the street in the
park in buildings etc. I have set Mic Attenuator to 0 dB. When I want
to have a clear recording with a peak maximum of -6 dB, I need to set
my record level to 2, which seems rather low to me.
Can anyone tell me at what record level he or she records??
I use a Sennheiser ME-66 mic.

I tried to use the -20 dB pad, but then I have to crank up the record
level to 8 to get a same peak maximum of -6 dB resulting in a useless
recording because of the hiss.

In an other thread one mentioned me to buy a mic pad of -10 dB, but I
first would like to know if it might have something to do with my
PMD...