Music Server Setup: Airport Express or Extreme?

I’m expanding my audio system to include other rooms in my apartment.

I’d appreciate some advice as to what the Apple Airport Base Station, Extreme or Express (or both together), are the best way to integrate this. I’ve been researching and considering this for a couple years, but it is time to harden my plans and ask specific questions. One area of confusion is with various Apple Airport Base Station models: I’ve read many conflicting reports regarding reliability/functionality benefits between the Express and the Extreme, so I’m a little confused.
I am on a tight budget now. I also want the Airport to meet my general computer networking functions as well as my audio needs.

Here’s the lay of the land:

I live in a multiple story pre-WWII residential apartment building in NYC (I mention this in case building construction effects wireless communications: my walls are plaster/lathe vs. sheetrock; ceilings are plaster and wire lathe; the wiring in the building is from an era gone by, so no contemporary in-wall network cabling, in fact most room only have 2 electrical outlets). With my laptop, I am able to connect with other wireless networks in the building, depending on location. My Internet connection is via DSL. There is a cable installed in my apartment but I do not subscribe.

I want to play music potentially into two other Satellite Rooms in addition to my main listening room: one of those Satellite Rooms shares a common wall with my listening room (perhaps I can just run speaker wire through this wall to power a 2nd pair of efficient speakers?). Another room is about 30 feet away from my listening room.

My main listening room:
Includes my analogue music rig and my desktop computer system.

Analogue Hardware:
I have a vintage Yamaha Integrated Amp, Meridian 508.20 CD player, Polk Lsi9 speakers, Music Hall MMF-7 Turntable, Kimber Kables.
Integrated Amp has 2 pairs of speaker outputs (one pair are unused).

Computer Hardware:
My main computer is an Apple G5 desktop (Dual 2.3 GHz PowerPC w/4.5 GB memory). NO airport card is installed in the computer.

My laptop is an Apple G4 iBook (1.33 GHz PowerPC G4, 768 MB memory, w/60GB internal hard drive). The laptop has an Airport Extreme internal card installed.

I have a dedicated external 500GB HD to store my iTunes music library (which is backed up to a second dedicated external 500GB HD). My digital music files are mostly Apple Lossless (with duplicates in AAC and MP3 files for downloading to my iPod).

My music server as it has been configured for the past 2 years or is an afterthought. It plays only in my main listening room and consists of the External HD (used to hold my music library) that is connected to my Apple G5 desktop computer with just an RCA splitter cable going from the G5’s audio-out to an input on my integrated amp. The Apple G5 runs iTunes. No aftermarket DAC, no remote controls. I control iTunes from the G5 desktop directly with a wired keyboard/mouse.

I want to do 3 things and in separate stages:
Stage 1) I want to pipe music into one other room, Satellite Room #1 (my bedroom). Satellite Room #1 shares a common wall with the main listening room and if need be I could run speaker wires through the wall to power a second pair of efficient speakers. ‘Background’ quality audio will be sufficient for now: I will upgrade the audio quality later as finances allow. I will only ever need to listen to music in ONE room at any given time.
Stage 2) add ability to pipe music into Satellite Room #2 (the living room). ‘Background’ quality audio will be sufficient for now.
Stage 3) Upgrade the DAC.

Remote Control Considerations:
I want to be able to control the music server remotely from any of the Satellite Rooms. For example, I would like the iBook laptop with its internal Airport Extreme card to wirelessly control iTunes (running on my G5) from other Satellite Room locations. What sort of Airport Base Station do I need to purchase: Extreme or Express? Also, does the G5 need its own INTERNAL Airport Card installed in ADDITION to the Airport Base Station?

Eventually, I would like to introduce a pair of speakers into Satellite Room #2 and have the same sort of remote control over the music server with the portable iBook as I have in Satellite Room #1. I expect for the Satellite Room #2, I will need to purchase a second amp in addition to speakers…but what other hardware would I need to get music into the third room? Or how best to realize this on a budget?

I may purchase an iPhone in the near future. I understand that iPhones (or even generic remote control devices) can remotely control the iTunes music server. If so, this would free up the iBook laptop in the event I need a second computer to run the system in one of the Satellite Rooms.

DAC Upgrade:
I’ve read on here much over the past couple years about DACs. Presently, I am using the internal Apple DAC built into the G5 desktop computer. I have read extensively about its limitations and after I get Satellite Room #1 operative, I will experiment with a budget DAC upgrade: maybe a Gary Nixon unit or a Benchmark USB. If an updated DAC sounds pleasing, I’ll sell the CDP and convert my system sources to only a digital music server and vinyl.

***I also want to be able to have the iBook and the G5 wirelessly networked together for general (non-audio) computing and file sharing as well, bear that in mind when recommending an Apple Airport model.

Thanks a bunch for any input or suggestions.

-Lovegasoline