It seems to me that most people don't consider the K1000 a good all around headphone, though many like it for certain attributes. I guess I'm in the minority, as I consider it an outstanding main headphone. I think Fitz is with me on this. I've had many headphones through my HF/HC journey, and these are the ones I knew would be my favorite main headphone for the unforeseeable future. It needs to be said though that isolation is obviously not an issue for me. In fact it's the pseudo speaker like qualities that make this headphone my all around favorite.
Amp selection is critical with the K1000. More so than any other headphone I've owned. It also scales extremely well. I love my balanced beta 22/K1000 combo. However after listening to them on a Woo 300B amp briefly, I think a high quality 300B needs to be explored. The bass extension with the 300B was anything but a subtle difference. Shocking would not be an overstatement. A good 10 watts would be important though, as the one I listened through was straining to keep up.
I agree that the Pass amps would be a good choice, as is the beta22. If money is a consideration try out some decent integrated amps as a substitute to headphone amps. Most headphone amps don't have the power needed to drive the K1000 well enough. I even heard them driven by a lower powered NAD integrated, with pretty good results.