I’ve always been very impressed with the sound quality out of the Bottlehead kits. Back in the late ’90s their company was called electronic tonalities, then at some point they rebranded to bottlehead. Strong focus on single ended triode, back in the early 2000s I brought my original Foreplay preamp kit they made available for like 130 bucks to a local Hi-Fi shop after the owner poo-poo’ed the DIY stuff - on reflection I don’t think that he actually expected me to walk out and show back up with a kit build- but a couple of the guys that had been hanging out at the store stuck around and were pretty embarrassed for the dude when my home built pre-amp sounded better and had a better soundstage than the very forgettable $15,000 something or other in his top of the line setup.
Since then I have built a number of their kits, perhaps my favorite is the Bee Pre, a 300B based preamp. Surprising because that tube is typically a power amp tube, the soundstage and detail is phenomenal, with nice full bass extension without the bloat you can get with a lot of tube designs I typically pair them with a fairly neutral power amp, currently a Parasound 21A supporting a pair of PSB T3i’s, although for a long time I ran a set of straight8 line arrays based (again) on a Bottlehead design which was another "punches far beyond it’s class" performer.
Some people criticize the Bottlehead kits on the basis that the sum total of the parts rarely exceed a quarter of the price of the kit, but I think the value is there with the quality of the instructions and also the attention that goes into the design.
A suggestion for someone who is interested and doesn’t want to overextend budgets or skill - the crack headphone amp kit is fantastic for high impedance cans, it puts out about 1/3w and is a very accessible project for a newbie at ~$300