How did the sound change going from Renderer without the Extreme to, I presume, the ProUSB with the Extreme? The differences I heard between the same comparison, but with using the Antipodes K50, were relatively minor, definitely not of the "wow, it's noticeably more realistic/believable/transport you to the venue or transport the musicians to your room" kind of thing.
The ProUSB had a slightly "cleaner" sound, revealing just a smidge more low-level detail, whereas the Renderer had a slightly more cohesive sound. Ultimately, both were great and would have been happy with either. The Renderer just allowed me to keep another box out of the audio room.