I ctrl-f'd through every instance of "augment" in the book. It seems that "augmentation" refers entirely to cyberware and bioware while to "augment" refers mostly to either enhancing yourself with 'wares (thereby reducing Essence) or AR.
Now there is a spell and a few adept powers that make reference to an "augmented (Attribute) maximum," which is where I think OP's question comes from in the first place:
The Attribute is increased by an amount equal to the hits scored, up to the target’s augmented maximum (any hits that would increase the Attribute beyond its augmented maximum are ignored).
Each hit on this test boosts your attribute rating by 1, up to your augmented Attribute maximum.
This power allows you to exceed your natural Attribute maximum, up to your augmented maximum.
This is different from the +4 augmentation
bonus cap. I think it all comes down to the following formula:
Natural Attribute Maximum + Augmentation Bonus Cap = Augmented Attribute Maximum
For example, the natural Attribute maximum for a human's Agility is 6, and the augmentation bonus cap is always 4. Therefore, a human's augmented attribute maximum is 6 + 4 = 10. Now suppose we have a human street sam character with a natural Agility of 4 and his augmentation bonus already capped at 4, giving him an augmented Agility of 8. He can still be further enhanced by an Increase Agility spell and receive up to +2 on his Agility to finally reach the augmented Agility maximum, despite already being at his augmentation bonus cap.
The only thing that throws me off is part of the example text in the character generation section, the only instance of magic being referred to as
augmenting something:
Now that she has selected her skills, she can go back and decide which ones will be augmented by her adept powers. For her Enhanced Accuracy [Skill], she chooses her Automatics skill, and for her Improved Ability [Skill] she chooses Pistols.
Because of this being the odd man out in the entire book, I believe this to simply be a poor choice of words where the writer should have used "enhanced," instead.
On another point, there's absolutely no reference to drugs augmenting anything, or even having a cap or maximum to their Attribute enhancements.