I did swap the tubes out for a while. Put some GT 7025 tubes in there for a less "tubey" more audiophile sound. But now I'm back with the original tubes. It's a nice box to switch tubes on because you can really hear the difference they make.
My bass playing friend modded his to change the impedance, I think he chaned it to 10k or something. I forget, I'd have to ask him. So it would work better with his particular pickup.
I have to say I loved the sound of the DITTO on his acoustic bass on this show we played together for several months. Just sounded great, an organic quality to the tone. You could hear the wood in the bass.