MondoArt
 
And still, the bass (kick and bass guitar) is never nice and tight and clear as professional mixes.
 
Basically, I want a good way to mix the bass, and thought mixing on headphones might help.  I still test on my computer speakers (with and without the subwoofer on) and in my car and on my bluetooth speaker and laptop too, but can never get the bass sounding really tight and clear.

From my point of view the challenge is the right balance between kick and bass. There is a nice way how to deal with that: https://www.youtube.com/watch?v=ECRx4WF3pcc
This guy explains a way good to realize way to deal with the right amount of bass (and in other videos, how to shape the bass freq).
 
Hope this will help you a little bit. Works great with the stock plug-ins...

Thanks, vdd. I've seen that video before, and in fact, I've learned a ton from Graham. Except that this technique as he described it didn't work for me. Granted, I used a free RMS meter, not the one he used, but the result when I did it was the bass guitar was WAAAY too quiet, it didn't make any sense.  I also asked him on his blog post if he does this after EQ and compression or before, but I didn't see an answer.
 
I find that even if I hi-pass up to 60 or 80 Hz on bass and kick, it still can sound muddy on systems with a subwoofer, and I can't seem to get it sounding tight as it does on headphones or my monitors.

Hmm, I use the tape emulation within PLAT to get the RMS meter and it works well.
Nevertheless, are you sure that the source of the muddy sound is the kick/bass track? I use a lot of high-pass filters (basicly at every track) to remove bass elements. All this bass sums up and can do a lot of harm to the mix. And because these are very low frequencies, you cannot hear them directly. At the end, it is like an additive synth: All the waves add up to higher volume/frequencies (but probably lower than 50hz).
I use the HPF at 30Hz with 48db nearly at every track which is not a bass/kick track by definition...
 

Yes, I hi-pass everything else, sometimes up to 250 Hz, depending. Thanks for the tape sim tip, I think I'll try that.