Highly debatable that edition XS is an upgrade.
And that smooth, addictive sound you hear with 6XX/650 is something very few (any?) headphones managed to achieve, the edition XS is not gonna be anything like that.
Many consider 6XX/650 best technical performer of the 3 senns above, many use 6XX/650 as their endgame because it is already a very strong performer and all the alternatives that may outperform it on some levels (Focals, some Hifimans, HD800, Beyer T1) all do so at the cost of that smoothness and near perfectly balanced response.
You can chase upgrades but you will be disappointed on some level.
Also dont really agree with getting a tube amp, they are just expensive sound enhancers, they can sound really great but they aren't making the HD6XX itself sound any better, which is what people seem to suggest.