External preamp for Marantz PMD 661?

["Bruce Rideout" rideout_bruce]

I record birds with a Marantz PMD 661, Telinga parabola with Sennheiser
ME62 mic, and a Sennheiser ME66. Despite having a great setup, there are
still times when I can't get enough gain to get a good recording of birds
making soft vocalizations. I'm wondering if an external preamp, such as a
Sound Devices MP-1, would increase the clean gain in these situations, or
whether my current setup is already as good as it's going to get.

Thanks,

Bruce Rideout