I have the First Watt SiT-3 with Klipsch Cornwall lV’s and this combination is my favorite over my Pass XA 25 and Golden Tube audio 300b…I put a 25 ohm resistor on the terminals of the Cornwalls… seemed to tighten things up just a touch. Sounds good!
I don’t know much the Heretics are, but I’d trust Herb’s ears. Bet they’d sound good with any of the amps listed above.