Configuration: KEF LS-50s, Schiit Modi Multibit Dac, Adcom GFA-555, Sys SB-1000 subwoofer, Minidsp 2x4
The bottlehead smash, despite not being mentioned much compared to the BeePre, sounds freaking awesome paired with the ls-50s. Every note has a lot more weight, transients are way more pronounced, the soundstage and positioning sound more accurate, dynamics are way more explosive, and vocals sound way more real.
On the bad side, the noise floor when paired with the gfa-555 is a bit audible, but not too bad. It goes away with 12dB attenuators - but at the cost of killing the dynamics a bit. I'm keeping them off for now, but may pop them on when I'm a bit less obsessive. Despite several folks on the bottlehead forums mentioning microphonics issues, I surprisingly have none. I preemptively bought lead weights and sorbethane feet, but I'm now returning them.
At low volumes this sounds like a mild upgrade to the Asgard 2 (and briefly the saga) I was using previously. But at high volumes, it is a massive difference. Everything is so much cleaner and fuller. Having recently tested the Saga, the sonic differences between push-pull and SET topologies is now very clear. The former is great if you want a clean, low noise-floor, SS-like sound with some soundstage benefits, but the latter adds a lot more tube effect to transients, note weight, soundstage, and tonality. I was a bit afraid that I would not like the tube-ier effect, but after the first song, I'm now addicted - everything sounds so real and natural.
Songs with great dynamics, like Miles Davis' Blue in Green, sound so close to actually being in my room. Thanks to the treble extension of the ls-50s, the sudden trumpet notes sound like an actual trumpet blasting in my ear. Vocal-centric songs sound surprisingly incredible, and I hardly have ever cared that much about vocal dynamics/performance. Artists like Listener went from great to jaw-dropping for me. The height/depth of the vocal position is much easier to discern, the vocals sit more consistently in the direct center, and the tone simply sounds more natural and real. Even cheesy (but awesome) pop-punk like The Front Bottoms sound like an actual whiney 20-something is in my room.
Somehow the bass sounds and feels more present while not being louder - it's odd to describe. Physically, I see the cones of the speakers moving more, but the bass isn't louder - just clearer. The edges of notes are also impressively more defined - particularly bass lines, guitar solos, and floor tom hits. I was concerned that the combination of an subwoofer (SB-1000 cross-overed with a miniDSP at 60hz) and a tube amp may sound a bit odd, but the low-end actually sounds a lot cleaner and fuller from the sub (which was no slouch to begin with).
As a project, this was really fun. The instructions and support from bottlehead are great. It took about 30 hours, including the smash up upgrade and troubleshooting two major stupid errors. I highly recommend their kits as a weekend project for anyone interested in diving into electronics without any real electronics knowledge. The folks that work at Bottlehead are genuine nerds that are excited to help anyone learn more about this hobby. You can DIY for cheaper, but the quality of instructions and support are worth the cost and make this a lot more approachable.
Here is a pic of the under side:
https://imgur.com/gallery/BKryO