The notes contained herein on your router being the propulsive engine for your inter home operations is true.
The DSL aspect only would apply to those machines drawing directly from the internet some audio of video stream (s), or other info/data.
Merely playing video or audio files from some networked drive on the premises and conveying it to some other networked pc or mac, has noting to do with DSL speeds, thru put, etc. thats all on your NIC cards/wireless adapters in your various wirelessly connected and networked hardware.
Please see:
http://compnetworking.about.com/od/wirelessrouters/f/bestwifirange.htm
80211G is fast enough to handle most any file type, IF CONFIGURED PROPERLY in the network adapter of the computer or device itself and theres no physical barriers to overcome via the signal broadcast freq.
What I think you need is either a stronger signal producing wireless router, or maybe, just a better antenna for the one you now have or for the units trying to cnnect to it.
Id also look into repositioning my wireless router. Ive used D link in the past with pretty good results. Im with FIOS and now have their Westell all in one router, modem, etc. only right in my office will I experience any issues usually . Thats where the Westell unit resides. Otherwise, I can stream/watch DVDs off a NAS drive via every pc I own now, any place inside or within reason, outside the home smoothly . Even with my 1.8GB CPU laptop running Vista!
For a time, I had a desktop using a D link USB wireless device. it was fine too in terms of connectivity and responsiveness.
Think about moving the router first, instead of replacing it. Look into the better antenna idea too. going up to N also means changing out NIC cards in each networked device if that is possible to begin with and not just the router itself!
Good luck.