DIY passive preamp idea

I would like a simple line-level volume control for my system. I currently have headphones, active speakers, and an active subwoofer. I want the speakers and subwoofer to have a volume knob before the line level output goes into the respective device's input. I would also like a mute functionality.

Would I simply get a potentiometer and hook it up between 2 3.5mm jacks? would i put a simple on/off switch for this sort of functionality too or would it cause weird imbalances? I was thinking at the least that I would buy a couple of alps blue potentiometers and a couple 3.5mm jacks even if I would need to turn the pot to the lowest setting as my "mute".

I downloaded the free version of eagleCAD and figured this would be a nice time to start learning that software with such a simple project.

I'll try to be a bit more specific. From my understanding, there are "active preamps" and "passive preamps". An active preamp uses active components such as op amps and such whereas a passive preamp will only use stuff like variable resistors and whatnot.

My audioengine A5's need a headphone-level input. my DAC provides line level output. I want to use essentially just a volume knob to control this volume and ratchet it down. Using software volume control is proving to be extremely annoying, especially for websites like youtube and such.

Similarly, my subwoofer has a line level input and has its own gain, but various songs and such have various levels of bass that I want. I dont want to have to keep crawling under my desk to adjust the bass level.

my idea was to either take 4 RCA jacks or 2 3.5mm jacks and put a potentiometer between them such as an Alps Blue Velvet.

In my mind, this should provide me with a simple volume control that will not introduce imbalance or THD/noise into the sound. My only concern is with the output impedance and whatnot. I dont want to screw up my A5 or subwoofer's circuitry because they were expecting a certain load and got something different.

I have no idea what i'm doing with eaglecad but I could probably draw out what I mean on paper if that helps.

Also, I have no idea how to implement a mute switch in this.

@eddieE: Yes, but this is what a passive preamp is. There are also active preamps that require power to function.
@nikongod: I have an AMB gamma 2 F++. You cannot drive headphones directly out of it because the volume control becomes an issue, so I use my Fiio E11 as a "preamp" and that way I dont really need to mess with computer volume. With the A5's and subwoofer though, they are both active components. The A5's have a volume knob but require headphone level input whereas my DAC only gives line level output. The subwoofer expecs line level output but I need to be able to control its volume without crawling underneath my desk every time. Also, when it is night time I cannot have the subwoofer on because everyone else in the house gets very angry. I am simply trying to make a passive line-level volume control for my subwoofer and speakers so that I can leave the speakers and subwoofer at a proper volume and then use that volume knob for quick and easy adjustments on-the-fly.

EDIT2: http://beavishifi.com/articles/Volume_Control/ This is basically what I'm looking for. I saw those goldpoint stepped attenuators and those are incredibly over my budget, unfortunately. So are their preamps, considering I need 2 of them ($300 each?!). I think i will take a look at the lightspeed attenuator and compare it to the alps blue velvet idea. Honestly I dont really need a "smooth" volume increase/decrease. I just need it to not make one channel louder than the other as the knob turns.
Edited by shrimants - 12/28/11 at 12:13pm

UPDATE:

I've been looking around and have seen various solutions. one is the above mentioned simple solution in which I take 2 headphone jacks and hook them up to a potentiometer. Another is to buy a stereo attenuator which gives a VERY nice prformance but costs around 150 bucks per attenuator. Remember, I need 2: One for my subwoofer and one for my speakers.

I found a couple of pre-made solutions such as the M-Patch 2 or buying 2 M-Patch nano by a company called SM Pro Audio. The M-Patch nano seems to be exactly what I need: a single stereo line-level volume control. The only problem with that product is that I need two of them. The M-Patch 2 is almost what I need but it has balanced outputs and those are of no use to me as of yet, and I would rather not try purchasing a balanced to "normal" cable.

There was another project article detailed on stereophile about a passive buffered preamp. I dont even know what that means and I have only a very basic understanding of what a buffer is and how it operates in terms of resistance. I didnt see how that can entail it being a passive preamp if it required a power transformer and everything though to power the buffer.

Further help would be greatly appreciated. I just dont want to spend 50 bucks on parts+enclosure only to realize that my idea was wrong. I was thinking I could simply do something like this picture:

Excellent. I have ordered 2 of the Alps Blue RK27 50k ohm pot from AMB's website, along with 8 RCA jacks (4 per source) and the mounting board and some headers for the pot. It should allow me to experiment with minimal to no cost to me. I ordered the crimp terminals too because I felt that I'd rather not blow 60 bucks worth of parts with a simple mistake. This way I can also use this whole assembly and improve on it and whatnot. Most people only use 1 preamp and this lets me basically get 2 into one container so I might be able to experiment with buffers and such.

My last questions are, what kind of switch should I look for to implement a muting functionality? And given that I have barely any tools except what my dad has lying around, what sort of enclosure should I try to make for this? And finally, what kind of knob am I supposed to look for?