I can only confirm the previous opinions.
I bought this F1-X in Switzerland but used to show, it dates from 1989, for a ridiculous price (400 €), I changed the tube 12AX-7 and it's perfect, round, hot ... not need anything else. http://alembic.com/club/messages/393/41288.html?1182802863
Simple crossover connection and integrated, usable or not (output mix)
With a 5 string Alembic Mark King and Stanley Clarke short scale (see Opinion Alembic Signature Deluxe). Ampli Yamaha P 5000 S, but probably baffles to define the SWR or when the HP PA full range.
For me it's perfect.
There is no other bass preamps worthy of the name ... others I had at the time were two F2-B Stereo.