do y adapters make you lose any quality

No - especially not with those pricey JL interconnects you are using.  Word to the wise - the wire you use doesn't really have any bearing on the signal quality - expensive wire enriches nothing but the seller.

This does make some basic intuitive sense - and I actually this is a real interesting statement just from a psychological standpoint - but anyway - no - low level signals don't work like that - I can't really explain it technically - maybe heamph or DYohn can - but it isn't like water in a pipe- it doesn't have mass that is being split up so it doesn't reduce the signal or degrade it or anything.  You could daisy chain 10 amps like that and they would all recieve a useable signal.

This wouldn't work for a 4-channel/sub-amp setup, but for subwoofers this is okay - you'd lose stereo seperation if you were doing it with 4-channel.

Naww man - its not like that - I went through a stuck-up phase and had all JL interconnects.  In a 93 Corrolla with 140K miles.  I dunno what I was thinking.  They cost me more than my 6-channel.   ... and more than the car itself!

Real nice wires to be shure - and didn't mean to offend - I just don't wanna see anyone waste thier money.  Trying to be - uhh - 'helpful.'

Think of your head unit's pre-amps as a high quality amp and the amp they're connected to as a speaker.

You know how a good amp can double its output power when the impedance is halved?

Your HU can do the same thing, but since the pre-amps have such a low output impedance compared to the rca inptus of the amp they can be split several times (each split cuts the amps input impedance in half) w/no significant loss of voltage.