I got a big jump in sound quality by adding three Synergistic Research ECT's ( Electronic Circuit Transducers ) to the amp. One ECT near the rectifier tube, one near the driver tube, and one near the volume control. Other locations that had no effect or a negative effect were near the output tubes, near the transformers, near the power cord inlet, and on the sides of the amp.
With the ECT's in the right location, the soundstage greatly improved and the harmonics were much more musical. I have had a similar improvement using ECT's with the Art Audio PX-25 amp.
I think this is a fun and worthwhile experiment with a product that has a 30 day return policy.
David Pritchard