I am demoing the Joule LA300 right now. It is a very nice preamp. Great microdynamics, and upper midrange. Compared to the Rex, the bass is not as articulate or defined. The Joule goes low, but the quality of the bass is not on par with the BAT. The Rex holds-up better with orchestral pieces. The Joule sounds excellent with smaller ensembles.
I have not made-up my mind as to which I prefer. I kinda want the upper frequencies of the Joule, and the lower frequencies of the BAT...