Hi Jonathan,
I'm not sure what I would do with only $5-600 to spend. I can tell you that I could not live with a passive pre. I tried various passives, including the Bent Audio and Placette, and I did not like them with the DeCappo. Its true that passives are very transparent but, to my ear, the sound becomes thin and lifeless. Several friends who have tried passives have eventually gone back to active preamps, particularly tubes, but your experience with a passive may be very different. Nevertheless, I think you would prefer a tube pre. Maybe a Bottlehead Foreplay (which I have never heard) or a used Audible Illusions etc. Just my opinion, of course.