Hello Natty,
To answer properly we have to go into rather specific details of these components and I do not believe that this is wide knowledge, so let me try to answer your question(s):
1 Joule-Electra is reality is NOT pure single ended preamp. This line stage uses a phase splitter to process the unbalanced audio inputs as two BALANCED signals thereafter dramatically reducing preamp induced distortions and then sum them together before the output.
2 Spectron stereo is not fully balanced amplifier. It has balanced inputs (w/XLR) and outputs.
3 Spectron monoblocks are fully balanced regardless of your input be it XLR or RCA - makes no difference.
4 I have read that you are particularly concern about the highs in Spectron. I believe its highs are very good as is but we also offer so called V-Cap upgrade where Oil and Teflon caps are installed into power supply for additional filtering - this produce even better (silkier) highs and midrange. There are other things can be done in amplifier to further improve it e.g. installation of four HiFiTuning rail fuses will add to "liquidity"
I hope I answer your "technical" questions.
Simon