How do I add another amp and speakers to my system. I have 3 pre-outs (1 pre-out for subs, and one for four channel amp running front and rear speakers) I'd like to add another 2 channel amp and 2 speakers. Will splitters work off of 4 channel amp?

https://www.pioneerelectronics.com/StaticFiles/Manuals/Home/VSX-D412_OperatingInstructions0224.pdf

Well personally i would probably use two channels to run all the highs and bridge the other two channels into one mono to run the sub ..

I guess you didn't get the owner's manual, huh?

http://www.jbl.com/HI-IN/Products/Pages/ProductDetails.aspx?PID=SCS200.5BK/230

Where are the amplifiers in this scenario?

Page 8: The sub needs a subwoofer Line Level pre-out from an AV Receiver or multichannel processor. Though not elaborated on in the manual, the L and R Line Level RCA connections are probably for use if you lack a Sub Out feed. Running L and R from your receiver would allow the sub to derive a Sub Channel.

The rest of the speakers would connect to the AVR's speaker outputs.

Pasge 9: Alternate method if your eelctronics lacks a volume-controlled sub pre-out. This method routes only the front speaker level power to the sub so it can extract something resembling an LFE channel, then it routes speaker wire out to the front speakers, not as an audio power source but simply as a pathway.

You still need amplifier channels for all but the sub.

My advice would be to connect the front speakers and the sub woofer to the amplifier and run the remaining rear 2 speakers from the headunit. This way you dont stress the amplifier to run on two different loads at the same time and still maintane control over your system. Bridge your sub woofer on chanel 3&4 and do not forget to set the LPF for chanel 3&4. If your speakers are not components in the front set the HPF on chanel 1&2 to roughly 60 to 80 Htz.
dreamsystems.

So you wanna run the subs off of the rear pre amp output rather than just the sub out correct? just get a splitter and run both the rear speakers and sub off of rear channel and front off of front channel. or run all four off of front and subs off rear output. this should give you the sound you want

run two 6x8s on each of the front channels of the amp. then depending on the sub you can bridge it on the rear channels.only if its a single four ohm. if its a dual 2 ohm sub run each coil on each channel. 1 coil-1channel. the other coil-the other channel. amp should run fine may run a little hot since it will be doing all it can do at a safe ohm load. just make sure it is mounted in a well vented area. should be safe.

The head unit will drive four speakers, 2 front ,2 rear.
Best way to add two more speakers and a sub is to get a 4 channel amp. Hook it up to the RCA jacks from your head unit. Bridge two channels of the amp to drive your sub, and use the other two channels of the amp to drive the extra two speakers. Just make sure whatever amp you get it's bridgeable.

According to the specs for the xo 1945- the output is; 50W x 4 Max Power Output , and I do not see a pre amp output listed. So I think to connect subs, you will need a separate AMP.
The way this works; the rear speaker wires from the xo 1945 hook into the Add-on amp, for example a 4 channel amp. In a 4 channel amp, the rear speakers come off two of the channels of the add-on, and the subs come off the other two channels. There is also the option of bridging two channels for more output power to ONE sub.
You did not mention what size sub(s) you were thinking of adding, but keep in mind that the ox 1945 puts 50 watts MAX per channel. So, if you add two 12" subs and a 1500 watt amp to drive them, your total sound is going to be very uneven.
If you go on line and look up auto audio or amps, you'll get a good idea of all the Sub and amp options that are available.... Hope this helps.

well yeah thats what im doin riht now in my ford taurs what u do is u can hook up your 5x7s and ur 6x9s on ur amp sill have room for a sub the way too do that is get the front speakers off the amp just run the back andsince its a four channlel amp 1 and 2 channel are used for the back and 3 and four are used for thesub of couse u brige the sub to the amp 3 and four are used for the sub hope that helps friend let me no what happens

Yes you can use the speaker output in conjuction with the rca pre-outs...but depending on the wattage of the amp, there may be a big difference between the loudness of the front speakers over the rear speakers. If you have a 4 channel amp you can put the rear speakers on the amp also and lower the input gain for the rear speaker. Or if you have a 2 channel amp, you could use a passive crossover to filter out some of the bass to the rear speakers since they are smaller, this would help prevent over-driving them...as it is normally too much bass that distorts and blows a speaker. I'm not sure what you are asking about the hi-rear preouts vs the mid front pre-outs. If you decide to use the amp for the fronts you should be able to connect the amp from the front preouts of the deck. Hope this helps.