I think the transformers made a big difference for the bass but initially the bass felt like it was soft. We swapped in larger Mundorf caps and wham! It was like adding half an octave of bass, and brought the performance within spitting distance of the EL34 amp. The caps added $600 to the build, but well worth it. Total cost was about $4k including the Gold Lion tubes.
I'm 100% in agreement concerning the vital importance of output transformer quality and better quality capacitors. I'm surprised that a SET of your amplifier's build was only 4K, seems quite the bargain from what I see. This is an amplifier that you'll have and enjoy for years I bet.
I've owned my 300b SET mono blocks for more than13 years and quite frankly my appreciation and admiration of them continues to grow.
Charles