Ok, this is probably an average joe responding and even somewhat off topic

I have recently ripped 2 cd's with the new aac format using the faac encoder and an open source ripper called bonkenc.

To my ears the quality is 'much' better then the rips i've done using the lame codec - maybe there's a new version out now, but i don't know.
1. The stereo is much better (using joint stereo on both)
2. The sound is much 'richer', i guess this is because the frequency range of the faac coder is just wider

So far for my opinion, now a few questions:

I've read most on the different acronyms (ltp - tns - sbr - ..) but would like to know which add to audio coding complexity (i.e. cpu power required) and which make the resulting .m4a file bigger? If there is a place where i can find this, pls let me know
I would also like a good explanation of what they all do - especially tns - in layman terms if possible

so much for my wishlist - anyone ?