No irony but with the statement "I'm not gonna buy a bass and i want to get those fast parts to sound decently realistic." the answer is already given,there's no way to make it sound as a real bass
"people know how to program MIDI drums to sound realistic even for extreme parts, so i guess there should be a way to do the same with fast tremolo bass parts."
That's because everyone is using triggers and the audience is used to that sound,so people add the same samples both on a real drummer and a drum machine.Also many extreme metal recordings are recording with an E-kit
So the "fake" cymbals are common in the audience.
If you want a r e a l bass guitar sound that will make your mix sound huge then a real bass guitar is needed.