I think there's a little more to it than just strings. I do use the Ernie Ball stainless flats (Group I, .055 to .110 tuned to D-standard), but what contributes is a Diamond compressor (or sometimes a FEA Labs Dual Band Compressor-Limiter) and a Broughton Audio high-pass filter. And for live thump, sheer horsepower is critical. You are not going to get any serious thump with a 30 watt amplifier.
Great points. The Broughton HPF has been my GAS list for awhile