A couple of practical points specific to your components: since your pre has an output impedence of 800 ohms, using the 1:10 rule your power amp should have an input impedence of at least 8k, which is easy to find. (My Alephs, for example, have an unusually very low input impedence of 10k ohms.) Secondly, and perhaps more importantly, use of a tube amp with a high output impedence (let's say above 1 ohm) WILL couple with your speakers' variable impedence differently as a function of frequency, resulting in the somewhat unpredictable trampolining of its freq response that can make tube amps so much fun (!?). However, a 6ohm speaker load min is pretty high, so MOST tube amps will show minimal timbral distortion. Again, think of the varying load response the amp sees as it's 1 ohm impedence meets a 6-20 ohm load across 30-20kHz window. (Yes, study ohm's law.) Then imagine what happens with a more common lower impedence load, often varying down to impedence minima of 2-3 ohms!
There can then easily be a 10x change in "load" across the frequency band, severely modulating the response. Usually the upper bass and mids get plumped up, the highs rolled off. Only works well a small percentage of the time since it's such a wild crapshoot. So even though your speaker is relatively amp friendly I'd chase an amp with a low output impedence to maximize your odds of a reasonably flat frequency response without having to tweak the hell out of your room, or other consequent bandaids. Good luck.
There can then easily be a 10x change in "load" across the frequency band, severely modulating the response. Usually the upper bass and mids get plumped up, the highs rolled off. Only works well a small percentage of the time since it's such a wild crapshoot. So even though your speaker is relatively amp friendly I'd chase an amp with a low output impedence to maximize your odds of a reasonably flat frequency response without having to tweak the hell out of your room, or other consequent bandaids. Good luck.