I hope you mean that the dbx box preserved the dynamics of those recordings you were capturing. Me, I wouldn't want the original dynamics altered in any way when taping (it audibly "pumps" if you push dynamic restoration more than 5-8%).
I can only tell you that, in general, my tapes sounded better than the source vinyl albums - especially those recorded 15 ips. Back in the day, I also used a dbx 3bx to tweak the dynamic range a little bit during playback. The sound was a little fuller with a tad more bass. I still have the 3bx, but I no longer use it.
As for recording your vinyl today, surely your phono preamp before the BHK has a fixed line-out. You could use a splitter cable at that point, send the signal to the BHK Pre AND the tape deck or dbx box at the same time. Then monitor your recordings thru the BHK in your chosen tape input.
I use XLR cables between my Stellar phono pre and the BHK. I may give the RCA cables with splitter idea a try. That would be a lot cheaper than buying a new preamp or integrared amp 😂!