I was surprised to realize I've been using my K-12G for more than 20 months...photos of my build are on page 3 of this thread. These days I think it's ugly but, hey, it sounds great!
In the beginning I was using a pair of Infinity Primus P162 bookshelf speakers, which were great. I then added a subwoofer I built following Gio's excellent project:
http://diyaudioprojects.com/Speakers/MAW-10/MAW-10.htmI had started out with Uriah's optocoupler-based attenuator but a few months ago switched to Bruce's Forewatt (DIY version in a semi-fancy wood chassis, photos to be submitted). No compelling reason for the change other than, well, change. I like building tube amps and if my efforts are successful, then change happens. Otherwise, the fire department is called.
A month or so back (while my wife was out of the country and I was without adult supervision) I bid on, and, much to my dismay, won a pair of B&W speakers (on eBay), the LM1 series (no longer in production). I have B&Ws for my home theater system's rear and center speakers (VM1 series) and love 'em. When the LM1s arrived, I swapped them with the Infinity pair, and find the B&Ws slightly better. I paid about $170 for the latter and probably close to the same for the former.
The combination speakers/subwoofer fill my office to overflowing, even with the volume at 10-15% (or thereabouts).
The K-12G is a good little amp that puts out lots of power, at lease in my estimation. If you are handy and can build speakers, go for a two-way, efficient unit (>88dB; seek the speaker projects page) AND a subwoofer. Otherwise, keep your eyes peeled for a good pair of bookshelf speakers, which shouldn't set you back more than $200 for a pair. There's another thread on this topic, BTW...I'll let you find it. That's only my opinion. If you have great personal wealth, then I think you should spend at least $2,000.00 on speakers for your $200.00 amp! Please buy American. Or Canadian. Hi, Gio!
I think I have, between the original K-12G kit, tube preamp, speakers, and my subwoofer, not much more that $650 invested in the system. Every person who has heard has been blown away...er, really impressed.