I used to use Sennheiser HD600s with my Fisher 400, but I sold them so I haven't tried them with my Meta. Still, I think I can compare the two amps pretty confidently. If your Meta uses Burr-Brown opamps, the Fisher will sound much, much better. Smoother by leaps and bounds, and just more musical. It's a closer match between a Meta with Analog Devices opamps and the Fisher 400, because the ADs are already pretty smooth. The main difference is that the Fisher lends a really magical quality to the midrange (I know this is almost a cliche, but it's true), and just in general the Fisher seems more refined and has a wider soundstage. On the other hand, the Fisher is a bit rolled off in the highs, and this isn't the most wonderful match with the HD600s, which in my opinion are already a little rolled off. Maybe since you already have a replacement cable that's brighter things might be just right for you. The Meta does have better highs. The bass on both units is also different, but not hugely so. The AD opamps really don't have the classic solid-state bass (which, IMHO, is a good thing), but I'd say that the Meta has slightly more solid bass, but the bass presentation is less realistic. The Fisher 400 also rocks with speakers, especially bright/harsh ones, because it sounds just right with them, not bright or harsh at all.