Suggested affordable quiet amp for high efficiency speakers

Hi everyone,
I had a question about the possiblility of implementing a subwoofer output into this amp.
By doing so, I will open up more potential subwoofers to purchase that don't have speaker-level inputs and only have a single RCA input.

My goal is to have the audio come into the amp via the RCA the binding posts at the back, go through the volume pot and then the output of the volume pot goes to the inputs of both the left and right channel amps for the speakers but also has a downmixed mono RCA port that can be connected to a subwoofer. I want the volume control of my amp to also change the volume of the audio going to the subwoofer so they stay volume-matched.

Am I correct in the idea that I split off the output from the volume pot, through a series resistor on the non-ground lead, one for both left and right channel, then join the output of the resistors together before soldering that to the RCA post at the back of the amp to be connected to the subwoofer?

I've attached a terrible ms-paint dialog of what I mean. Scenario 1 is what would normally be set up, and scenario 2 is the one I am hoping to do.

Also, would the 220ohm 2w resistors I have purchased also work for this case?
Subwoofer Output.png

The kind of subwoofer I am talking about is something like this:
Subwoofer with only RCA Input.jpg

Thanks for your help!
I almost have all the parts delivered, but I wanted to double check on the mods you mentioned are good to do with the amps.
I have attached a picture below. I know I need to remove the SMD output caps, and solder a leg of each of the blue caps to the output of the black things on the board, join the other leg and connect to two parallel 2w resistors, but where to I solder the output leg of the resistors to? I can't tell from the picture you uploaded in the other thread.

Thanks so much for your help!
Joined 2008
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Ah thanks Preamp, I'll double check the wiring of them. It was just a rough diagram, I'll make sure I get the correct cables in the right spots on the potentiomer.

HAYK, just to double check what you mean, I've completed the diagram as far as I understand you have explained it.
If you say it looks good, I'll be able to get the soldering iron out soon hehe!
I've attached the final guide below.

Thanks again for all your help and I'll post back with more progress as I have it!
Amp Mods Final.jpg
Hey bros, just a small update - all the parts have arrived! I will attempt to fit everything into the smallest case that I found that can just fit everything!

This is the case that I chose:

I have 3d modelled in FreeCad a base plate that will hold all of the PCBs that make up this amplifier and facilitate easy connection between the parts.
It is printing now, I'll see if the print worked overnight tomorrow and whether I need to make any changes to the tolerances and reprint.

I'm also toying with the idea of 3D printing the backplate as well, rather than bothering to drill through the aluminum. Might end up being easier, I'll see!

FreeCad Snippy.jpg