Two Sub-out Preamps - Need Y Connector?

I have a pioneer 4100NEX with two sub preouts and an infinity 704a 4 channel amp which I will be using as a 3 channel (sub bridged) which has two preamp inputs for each side.

The infinity manual does not state anything regarding mono input, so I am not sure whether I need a y connector or even which preamp input is to be used for mono hookup. Anyone know?

Is this something that I should be contacting Infinity over? The manual shows how to wire outputs in bridged mode, but ignored the input question completely.

 

Anytime you wire any two channels in bridged mode (mostly) the output is summed and is mono.

 

Regardless of anything there are two major parts to this. Make sure that one input is not separated from the other as for high and low crossovers built into the amp. Second and most important. At no point should you be using a Y-adapter to run RCA or any cable carrying signal to the amp. The only thing you do is introduce a new splice into the system and when you split the signal while still in the pre-amp phase you are splitting the Voltage. Which destroys the end result. Volts in comparison to watts is a ratio that is too large to remember here check this link. Explains way better than me.
http://www.audioholics.com/audio-amplifier/amplifier-voltage-gain