Need to run 8 RCA's to 6 in the back of the head unit, please help

[HowlingThrone]

Hi all,

I apologize I am newer to the car audio thing, I have a 2016 nissan altima, did the big 3 upgrade, already have all the wires and power ran to hook up the system, here is where we are stuck.
(I am sorry if i get some of the terminology wrong)

I have an Alpine that has 6 channels, (front, rear, sub)
I also have another amp that is the mono-block for my sub

I have 9 speakers in total to setup: front tweeters, 4 door speakers,2 6x9 in the rear deck and the sub
we were planning to connect my front and rear door speakers to front Left, and front right, the 6x9's to rear left and rear right and then we wanted to use the Tweeters on the Sub channel of the amp and then we would just connect the Sub to the monoblock

the way we looked at the power usage of the Alpine is, I can get 75 watts (RMS) per channel on the 4 main channels and 300 watts (RMS) on the sub channel
The Tweeters are 150 watts (RMS) each so it equals up to the 300 watts on the sub channel and then the door speakers are only 30 watts (RMS) each so combined together thats only 60 watts and then the 6x9 are 90 wattts (RMS) each but my roommate said that should be fine because its close to 75 watts.

Now my one roommate is helping and he is decent at car audio but wasnt a 100% sure and my other roommate who is the big car audio guy and custom installs all of his stuff and was helping/doing it has been really flakey lately and so we are just trying to get it done.

The main issue here is, My new head unit is the JVC Z1000w and it has 6 RCA inputs in the back. (front, rear, sub.)
How do I connect the tweeters?....I basically would have 8 rca's total, (Front, rear, sub, tweeters) and I cant just connect the tweeters to the front left/right at the amp because the skars are 150 (RMS) and the normal channels are 75 in total (60 being used up by the door speakers)

Thank so much for any help you can provide.

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[HowlingThrone]

Can I use a female (2) to male (1) Y adapter? Essentially, take the front left RCA and plug into one side and then plug the (Left) tweeter RCA into the other side and then plug the single one into Left Front?

Or even the reverse 2 males to one female, plug one into the left front and the other into the sub left and then plug that into the set of RCA's running to Head unit

 

[chillin 10+ year member]

So you're planning on running active and using the amp or head unit crossover for the tweeters?
Is that sub channel full range and have separate left and right or is it mono?