Jp,
I am using the balanced Promethius Ref 4 TVC into a pair of older DNA-1 monoblocks with very satisfying results. My monoblocks are an older pair with 100 kOhm input impedance. If I recall, most of the later revisions by SMc audio use a much lower 10 kOhm input impedance. If that is the case with your rev a, you might want to stay away from the resistor based passives like the placette. TVC's like the Promethius might be a better way to go. I can't comment on comparisons with active pre's because I've been using passives for the last 15 years. In the case of the Promethius, its an inexpensive experiment to give one a try.