Wow! Thanks for all of your explanation! My line 6 HXFX just arrived and I just followed your instruction and surprisingly it sound nice! I already tried 2 signal chain thru DI and the Amps and yes you were correct there's a lil bit of "coloring" on the amps because of the power amp but It is not a big deal.
And yes I put the last reverb on my Nux because I don't do reverb all the time and it is not my main sound. So yeah, like what you just said if I want to make the sound of my pedalboard as flat as possible the best option is using a SS amp or an FRFR.
Once again, thank you for all of you helps and explanation.
Cheers!