dual xpa4100 4 ch amp

DUAL XPA 4100 rated at 600w peak (yeah right!!), now according to the manual it will put out 150w x 2 @ 4ohms in bridge mode. That's fine, but since my deck has only one 1 rca cable output for the subwoofer, i put a Y-cable so I could run left and right rca's to both channels, ch1 ch2 and ch3 ch4.

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The manual says; Select 2 CH mode if the head unit only has 1 pair of RCA
outputs. Plug the RCA’s from the head unit into channels
1/2 or 3/4. All 4 amplifier inputs will receive a signal.

Am i to understand that ch1 and ch2 are the ONLY rca's that need to be used and ch3, ch4 left blank? Again, i want to bridge my amp for my 2 subs.In bridge mode ch1 and ch2 are bridged (sub 1), ch3 and ch4 are bridged (sub 2). Question, should I select 2 channel or 4 channel mode, right now i have it 2 channel mode.

yes you only need one and 2
3 and 4 are for when its in normal 4 output mode
but mono 2 output mode
i takes channel 1 as positive and the outputs for 3 as negative as a combined output through the 1 channel
same with 2 and 4
so ya only need 1 and 2
if your not using a preamp good one at that and just using the right or left without balancing with the other you will lose input on that channel inporpotional to the other
it will mess with the sound quality

Thanks for the response, so to be clear, rca's only go to ch1 and ch2, then set the amp to 2 channel mode, bridge the amp and 150w x 2 @ 4 ohms will go to the subs.
Will give it a try!!
Ron

You need to connect the radio front RCAs to channels 1/2
Connect the sub out and the y adapter to channels 3/4.

If you feed only 1/2, you will not be able to utilize the sub output controls of your deck.

Not quite understanding what you mean, the Pioneer deck, deh6300ub has. 2 rca's for front, 2 rca's for rear or sub out when configured that way. You want the front rca's from the deck to connect to channel 3/4, sub out to channel 1/2.......you lost me.