[PStamler]

Here's an experiment to try.

Get some 3M StripCslk, sticky stuff used to seal windows.Using the StripCalk, attach the DPA's capsule to the brace under the fingerboard, below the 1st string. Let the wire come out the hole for now.

Try this as the mic component, using the pickup for reinforcement and monitoring as you're doing now. If you like what you're getting, attach the head amp assembly to the strap with some Velcro. If you don't like it, try moving the mic a bit, so it sits under different strings. If you still don't like it, take apart and try something else.

This has worked for me for some 20 years, admitttedly with a small steel-strung guitar rather than a classical. Give it a shot.

Peace,
Paul