Does anybody know the total length of the y-connector cable. I am looking to split the signal to the amp. As my pre-outs only have a L&R

Usually a Y connector only has a few inches of cable on each female end. If you need more length you add a standard RCA - RCA patch cable to one end or the other. If you are splitting the output of the preamp you would generally connect the adapter to the output of the preamp and then run standard cables to each amplifier. However, it can be done the other way, with the adapter connected to one of the amplifier inputs and the ends of the adapter connected, respectively, to the preamp output and the other amplifier input.

I make no claims about the sonic qualities of this arrangement, only that the signal will get where it needs to go. Be sure that you have only one signal source no matter how the devices are connected.

I may end up with this type of connection for two of my subwoofers, as I'd like to reposition one and with the configuration of the viewing room I'd have to run the signal cable across the floor in the main traffic pattern of the room. Daisy chaining from the other subwoofer input allows a much nicer cable routing along a wall.