Yet they sound perfect and well extended when driven by my big current pushing solid state monoblock amps.
'Current pushing'? This sounds like a misconception to me.
Again, Martin Logan is specific about the amplifier to use with their speaker because they have made the speaker so hard to drive. 0.5 ohms is hard on all amps, not just tubes! What you want to consider is how the amplifier distorts when presented with a low impedance- and in this case, **all** amplifiers, tube or solid state, will have higher distortion which will result in brightness.
I suspect this is why Paul Speltz got a letter from Steve McCormick, wherein Steve described how even though his amps can drive 4 ohms effortlessly and with double the power of the 8 ohm load, the fact was that they sounded better (smoother, greater detail) when using the ZEROs to drive the same load.
The simple fact is that you don't want an amplifier to work hard- it will have greater distortion which is to say it will sound harsher and with less detail.
George, you should give a set of ZEROs a try with your Rogue amplifiers. I think you will find that by using them, they keep up with your solid state amps in the highs. That is the experience of many people using the ZEROs. The ZERO website (
http://www.zeroimpedance.com) has many comments in that regard.