The power amps where it's at IME. A valve pre, sometimes of less than ideal resolution, transparency and tending to "round things off" somewhat, can make a typical "par for the course" SS power amp sound rather more "friendly" and "warm" but two wrongs certainly don't make a right... a REALLY good power amp, that doesn't sound "flat", "grey", "sterile", "hard" etc with a genuinely transparent pre (whether valve, SS or passive) is a much better proposition that will get you much closer to the music IMHO.
A good valve amp, EL34's to allow for Sara's being not the most efficient etc, on its 4 Ohm taps, should do just great. No current limiting from protection circuitry etc when the going gets tough
Something of Radford STA25 standard with good engineering and plenty of negative feedback by valve standards ideally. Naim amps have a 0.22Ohm resistor at the output and a damping factor of only around 16 with 4Ohm speakers.. an STA25 will match or beat this!
Many of the modern "lets make it really valvey and use only 10 dB feedback with cheap transformers and if it then has 2% THD and a damping factor of 3 than that's even more pukka valvey" would NOT do! EAR-509's would laugh off Sara's.
On the Croft thing well I made many past posts about what the driving capabilities are and what distortion to expect into various loads and why output impedance and ability to drive real loads often don't "match up" with valve pre amps etc in older threads...