A lot of clarifying rules were left out in SR6 (to save word count) but I have no reason to believe that the intention should have changed from the 5th edition.
In 5th edition headware could either take up essence (if installed inside your natural skull, even if you also had a cybershell around your skull) or (if the augmentation had a listed capacity cost) as capacity in a cyberlimb (any cyberlimb; skull, torso, arms, partial arms, hands, legs, partial legs, feet - but not cybereyes or cyberears).
Bodyware and cyberweapons could either take up essence (but only if installed inside your natural body) or capacity in a cyberlimb (but only if your limb have been replaced by a cybernetic limb and the augmentation had a listed capacity cost)
Cyberlimb accessories always only take up capacity (never essence) in the cyberlimb they are installed.
Eyeware either take up essence (if you still have your natural eyes) or capacity in cybereyes (if eyes had been replaced by cybereyes, eyeware don't fit in cyberlimbs such as cyberskull, torso, leg, arm etc).
Earware either take up essence (if you still have your natural ears) or capacity in cyberears (if ears had been replaced by cyberears, earware don't fit in cyberlimbs such as cyberskull, torso, leg, arm etc).
So you could for example install a commlink in your left leg and a cyberdeck in your right arm while a smartlink (which is eyeware) would either be installed as a natural augmentation to your natural eye (if you still have your natural eyes) or take up capacity in your cybernetic eyes (of your eyes are replaced by cybernetics eyes).
However, from a strict reading of RAW this is not very well explained (but it is also not contradicted).
SR6 p. 285 Eyeware - Cybereyes
...as well as Capacity for vision enhancements.
SR6 p. 285 Earware - Cyberears
Cyberears offer ... Capacity for modifications and enhancements.
SR6 p. 290 Cyber Implant Weapons
Weapons can be implanted into cyberlimbs, costing capacity, or directly into flesh, costing Essence.
SR5 p. 451 Headware (this rule is missing in SR6 but is assumed to still be intended)
Items that have a Capacity Cost [in brackets] may be installed in cyberlimbs instead, costing Capacity rather than Essence.
SR5 p. 454 Bodyware (this rule is also missing in SR6, but is assumed to still be intended)
Bodyware cannot be installed into cyberlimbs unless it has a Capacity cost [in brackets]. Bodyware with a Capacity cost can be installed in cyberlimbs, costing capacity rather than Essence.