Terry,
The truss rod cover is plastic - standard issue on set-neck Alembics. For a little upcharge, you can probably order an instrument with a brass truss rod cover, and probably in ebony too.
Your PJ activators probably came with the Low Pass Filter, rather than a set of bass and treble pots. Check the FAQ section for an explanation of the LPF, it is a different approach from bass/treble controls.
The Selmer may not handle the active signal from the Alembic electronis too well: it was designed for passive instruments. I remember playing through a Selmer ages ago, with a passive bass. Sounded nice and warm, but volume and dynamics were limited.