I replaced my stock speakers in the stock pods and got a noticeable improvement in sound quality. By noticeable, I mean that when I had the stock speakers still on one side and the new ones on the other side and I stuck my head in the footwells, the stock speakers had a much thinner, tinnier sound with little bass. The others were 'better'. Unfortunately, the Massive brand speakers I used for their thin design are no longer available. I found mine on Ebay after they were discontinued. I still had to cannibalize the pod and do some trimming with the Dremel, drill some holes and work at getting them in. The other thing I did was connect the mid-range speaker to both the high and low pass on the crossover that is inside the stock pod to get the best sound (don't remember which I used). All in all, I got my $130 or so worth, but I don't have monster sound by a long shot.
I thought the SSV front pods might be an improvement over my setup by using a 6 1/2" full-range speaker instead of the separates, but feedback from others has me questioning this.
As a rock and roll drummer and enthusiast I've always had killer sound systems but I just haven't justified the expense to put one in the Sling. I enjoy the music when cruising around town by myself, but on the open road the experience becomes about the road and quite frankly, quality music would be more volume than I enjoy anymore. I have the upgrade on my wish list and with a set of hoop pods, speakers for the pods, an amp and a powered sub, it's a $600-700 expense. For that, I'll have better quality and more volume, but if I want to cruise with awesome tunes, I jump in the Vette, pull off the targa top, crank the Bose system and burn fuel.
Life is good! How ya doing Brent? I'm hoping we get the chance to meet up again at some rally or another and I can check out your boosted Sling!