Why Don't We See More High Current Electronics?

I appreciate the discussion of amplifier topology and performance. It's informative for electronics novices (like me).

An amp with high input impedance is important

not "dry" or "lean"

lively with bass weight and clarity.

An issue is my Cary SLP 05 preamp has fairly high output impedance into the lower frequencies. My speakers are Mirage OMD 28 /Impedance 6 Ohms nominal /3.5 Ohms minimum 87db efficient /Crossover Point 550 Hz and 2.5 kHz

I hate to repeat myself, but a Threshold S500 with new caps and a re bias appears to be just what your looking for. Though Threshold made very well received pres, many used them with tubed Audio Research and some used tube c-j pres. If memory serves me correctly the input impedance was 75 KOhms. 250 Watts per channel 8 Ohms, 500 Watts per channel 4 Ohms. 20% Class A bias into 8 Ohms. Class A bias halving as power doubles into 4 Ohms.

Assumed you had some kind of passive. The 400 ohm Zout of the Cary should not be a concern even for an amp with 10Kohm Zin.

The 3.5 ohm minimum (4.25 - ultimateavmag) of the speakers isn't that critical either, unless it's coincides with a big phase angle, which it doesn't on those. In fact, they tend to be a little midbass heavy, peaking with the minimum impedance at about 90 Hz. Yes, they benefit from the bass control of a strong amp but, along with the titanium tweeter and some high frequency fluctuations (sibilance?), I think you're going the wrong way. Although, you could do much worse than the ones mentioned.

Thanks Unsound and Ngjockey. Unsound, at the time you referenced the Threshold it had a Sale Pending- I saw it before and it was Sale Pending for quite a while. I would likely have jumped on it.

Ngjockey:

From Stereophile's mearsurements of the SLP 05:

"The SLP 05's output impedance is specified as a usefully low 400 ohms. However, I got significantly higher values for the unbalanced output of 1500–1600 ohms in the midrange and treble, rising to 3400 ohms at 20Hz, with similar if slightly lower figures for the balanced output."

That seems like quite an impedance swing from the Cary. I'm not sure I would want to be married to it.