Saw your edit - don’t bother chasing power specs. The Magni+ will be a side grade for the money (and you’ll still need to stick with the Zen DAC to feed it), so I’d focus on going up the headphone chain since the Zen DAC should be enough for most upgrades.

If you can go and listen to a THX amp before buying, they seem to be in the same polarising camp like Topping where they measure extremely well but can sound worse than cheaper still good measuring but less focused on chasing analyser SINAD amps to some ears. Never heard any so can’t say if it’s as bad as some say.