With my limited experience, I agree with zlone about decay and equalization. For perhaps some tube dimensionality within and between your Benchmark system I’d be curious how something like a Modwright Analog Bridge would sound. I’ve never heard myself, but I’m intrigued.
For tube equalization, the Decware ZRock3 seemed to add a slight increase in dimensionality and space, while allowing a somewhat broad adjustment to the lower end. I think it would be a stretch for me to say that this perceived dimensionality also included decay, though. Unsure if I would have explored this option if I had a tube preamp tbh.