This wasn't my idea but a good point was raised that it isn't stated explicitly in the rules.
Q: If you put multiple Audio Enhancements Rating * in earbuds+headsets, or multiple Vision Enhancements Rating * in contacts and glasses, do their effects stack?
For example, if I got an Audio Enhancement Rating 3 and an Audio
Enhancement Rating 2 equipped, do I get +3 to my limits (and with wireless to my dicepool), or +5?
I would say no. Audio Enhancement Rating 3 + Audio Enhancement Rating 2 != Audio Enhancement Rating 5. Audio Enhancement is Max rating 3. (pg. 445)
RAW per SR5, pg 445 one sensor is max rating 3. The question at hand is what happens when you feed the output of one sensor (say headphones with Audio Enhance rating 2) into another (earbuds Audio Enhance rating 3).
It's not unheard of, in RL. (
http://en.wikipedia.org/wiki/Preamplifier). I guess it depends on RAI (what rating really represents? signal clarity or volume?).
Even though everyone thinks this is a phonebook case, I disagree on that. It merely allows more creativity for the players if allowed, or clarifies the intended use of the equipment.
I would like also to remind you that this could be vital info for riggers, since they could potentially rig sensor setups for ambushes and safehouses with relative ease on the cheap (I guess that would be an INT+Hardware check) and then use that for ultra long range eavesdropping (add directional mic, tada!). Even better, running around with a spy-van trying to pick up info on corp-sec from the parking lot across the facility sounds very trenchcoaty to me (a part of SR I love to bits).
Again, it's not unheard of for people to try to get info from as far away as possible using arrays of equipment. (
http://www.space.com/16000-spy-satellites-space-telescopes-nasa.html Go read about the capabilities of those babies NASA got. They were the spare/obsolete ones).