im new here, but not new to recording. I think a lot of the things in that post were good advice. I would not reccomend high passing your guitars that much though. He did mention he was better at mixing funk then rock though, and that may be a reason.
for guitars, each mix is different (of course), there are no rules to follow, but I usually start my high pass filter at 80 and adjust upwards to taste. that usually ends up being around 120-150..I have never cut all the way up to 250..that is a bit extreme for rock especially. remember the guitar is a midrange instrument.
also, for bass, between 200-250 is not a bad frequeny. I am a pro bass player and have been mixed by some really great engineers and learned a few techniques...id reccomend doing your kick/bass duck around 100-150...the bass has a lot of character in the 200-300 range, and while it shouldnt really be boosted, it should not be cut either. I rarely EQ my bass at all, except to adjust for the kick and maybe add a little attack between 1-3k somewhere to compensate. once again, when it comes to funk you can scoop mids a little more to compensate for slapping, bt i dont even do that if/when i slap..i keep it all flat and use a fender jazz bass.
a good way to get a good cutting bass tone is to duplicate (not double) your bass take and grab that copy and high pass it up to around 900hz..reamp it through a little guitar amp or amp sim and add a little distortion. mix your main bass track as you would, and then bring this duplicate track up in the mix until you get the attack you want...this is a pretty common technique that is used all the time..there are many ways to utilize it though, so be creative.
finally, im not sure but it seems like he said the vocal gets harsh at 2-4k? uhm, use
a desser if that is a problem, but don't cut those frequencies w/ an EQ. that is where some of the best energy in a vocal take comes from.