Hmm, interesting. I wonder if there was a setup issue with the D20R...though I notice you aren't saying it doesn't have bass, just not enough at low volumes.
The B60R will stay; I love the amp too much to sell it. But, I am really enjoying the Audio Space. Tubes and ProAc are a great match and this amp gives a really clean view into each performance, allowing me to hear each individual part but presenting them in a way where they fit together. So if I want to focus on one thing I can, but then I can pull back and listen to what all of those parts are doing together. I'm now leaning towards a quad of Shuguang Treasure 6CA7 tubes, along with my NOS RCA's. I am digging the EL34 sound more than I thought I might.