Its actually the opposite! The WA5 has more than enough power and dynamics to let the HE-6 have it! There’s 8-10 (roughly) watts out of the 300b tubes and the synergy is perfect with the HE-6! As good as Wa2/T1 combo, was a huge upgrade when I got and decided to call it my endgame, I’m too happy. I use the setup for speakers now but still have the He-6 as my ref headphones, organic with bass and clarity that nothing else has really come close to sounding for me. The GSX mk2 is good for He-6 too but seems a lil underpowered esp in the bass and sometimes the highs, not just volume cos thats alright, but it clips soon and cos its an ortho can, clips different than underpowered dynamics do, which just dont get loud. it works alright for fun but can be a hot mess at louder volumes, and the treble is more biting as the he-6 need warmth in the audio chain to work best. I love using the GSX as a preamplifier, more power coming out of the wa5 and boosts the dynamics up as it takes the power load off the 300b tubes somewhat when driving speakers. my speaker setup (using Omega RS8’s and sub) has never sounded better, I get the full 300b tube experience and the effortless liquidity and transparency of the gsx, they pair amazingly together! funny how this is all headphone gear, but ended up being used with high efficiency speakers, with amazing results! The gsx is the perfect under 3k preamp and the wa5 the perfect 300b SET class A amp under 6k! currently upgrading my dac (new mytek brooklyn dac+) , upgrading the sub, and adding a gyrodec turntable soon for analog source as well, then my setup will be complete! as for your question, both have great tone, the GSX just reveals everything so the tone matches your gear, the WA5 warm sweet and expansive, they work very well together, though few own both. I am considering buying a WA33 with preamp and speaker outs for that purpose, with headphones secondary, and I could use a 2A3 amp, but too happy with my WA5 its what I’ve always wanted and it won’t ever be sold! Waiting on the WE300B reissues as well!