The REGA Osiris integrated amp is one of these exceptions. While it is a beefy hi-current and high WPC amp that doesn’t fully double down, it still has LOTS of current because of its high-end build and design. This is provided by those four Sanken output transistors per channel, that insure that no speaker is too hard to drive.
This statement is incorrect. The extra transistors make sure the output section can support the current without damage but if the power transformer lacks the current capacity it really won't make any difference.
To me, a big honkin’ transformer (sorry Ralph) and the ability to double down to 4 Ohms and maybe double again down to 2 Ohms is a good indication an amp has the balls to power most speakers
This is generally correct but if the speaker does not have any low impedance dips it could be a waste of money, especially on Maggies which do not have such low impedance dips.
I should point out also that not all speakers that dip to 2 Ohms need a lot of current capacity in the amplifier; Wilsons are a good example. They can easily be driven by tube amplifiers even though the low impedance dip is in the bass. Generally speaking Wilson loudspeakers have traditionally been easy to drive.
If I can point something else out: Just because your amplifier can drive to 2 Ohms and is able to double power as it does so does not mean its sounding its best when doing so. All amplifiers make higher distortion when driving lower impedances! If you think that distortion is inaudible think again- the increased distortion is audible as increased brightness, harshness and a reduction of detail (distortion obscures detail) because most of that added distortion is unmasked higher ordered harmonics.