Ecruz, I would move it upstream. But as far as "I don't want to mess with the amazing sound from my Sony/TRL 900," as Kenn and El have pointed out, you already have messed with it by interposing the Behringer in the chain. There is no way around this, regardless of whether the Behringer is fore or aft of the preamp. But, having messed with it, if it still sounds amazing to you, you might as well mess with it some more and explore your options.
I have two digital sources going into the Behringer, a CDP into the Behringer's optical input and a Monarchy DIP (which itself has two sources, so I guess that's three altogether into the Behringer) into the AES/EBU input. I select between the two by using two programmed presets that differ only in terms of the input source. That may be the kind of arrangement you are thinking about?
Drubin, I haven't been able to read through that article without my attention wandering, but I don't think the author was talking about overlaying target curves. I think he was suggesting choosing an all-purpose target curve (even flat) for autoeq and then overlaying other programmed "psychoacoustic" or "personal" presets at the playback stage to try to improve on the sound. Then, if you wanted, you could use the knowledge of which of these overlays produces a better response to set a new target curve and redo the autoeq process. Actually, this is the approach that I used--started flat (except at the low end since my speakers are short of full range) and then overlaid adjustments from there.