260X is a 7790 and about same performance such as a 650 TI OC (there is OCd out of the box cards) or a 650 TI boost, so those cards arnt "low end" they are challenging the 260X, thats fact. The aged 6950 is at least comparable in performance and the 7850 is a bit ahead, not by that much but they got the edge as far as i can tell. On top of that the 6950 can now be gotten for very few bucks, so price/performance is higher. Regarding AA, the slow memory bus and low ROP count of the 260X is able to cut its wings, and in term of high AA, even the 6950 may outperform that card. So its a rather mediocre gamer card and Nvidia got comparable offers for a full year already.
I think, regarding audio quality, we have to separate the "physics" from the "general" audio quality. The physics itself isnt general audio quality, but even the physics quality is increased a lot when there is good audio equipment resulting into general quality. Its possible to use headphones and hear a noticeable "increase" regarding sound physics but its still no match compared to real audio equipment.
So, there is probably not much general audio quality needed in order to hear "good sound physics", as long as that kind of physics isnt much more than the increase or decrease of noise in order to create a audible space. But even more complicated when the exact direction of a sound have to be executed. Gonna be hard with just 2 speakers, but according to AMD they can do magics and create the audible space out of 2 speakers or a pair of headphones, and that makes me officially impressed. Prehaps they was boasting to much, i cant say without excessively testing it. I think a majority is simply underestimating the sound matter in general and got in mind that they can get good sound without serious investment. It may not work that way because audio equipment is just as important than a good monitor, as far as my knowledge goes. As far as my experience goes, especially when it comes to the implementation of the exact location of sonic waves (this is part of the sound physic), even real high end 5.1 and 7.1 systems are challenged doing so and even the room itself is very important, it will need a good acoustic.
But in term AMD is able to do magics and bring some outstanding sound physics to everyones ears... i will just gladly shake theyr hands and bow down.
as for the load on the cpu im sure it will be very minimal, idk what the main cpu of the system would have to do with it besides assigning it minimal resources the gpu will be doing all the calculating.
Most of the sound physics is currently done CPU side not GPU as far as i know. The GPU is usualy busy at rendering and sometimes visual physics too (Havok, PhysX, TressFX). Although the sound physics development has been stuck for some time, a CPU simply got its limitations handling it. So the devs didnt pay a lot of attention to sound physics anymore, thats at least the stuff told by AMD. I cant tell, i never made research regarding sound physics but i find it a interesting and important matter with a lot of possible improvements.