Here's a difference that I don't think you'll find apparent in the specs: the finish. Now I haven't compared the S38 and S38II side by side, but I have seen the original in BestBuy and own a pair of II's. In my opinion the finish in the II's is significantly better than the original S38's. Not because it's more durable or better sounding, but simply because I think it looks much more appealing to the eye. For some reason I thought the ones I saw in BestBuy just looked horrid, the "grain" just stood out far too much and didn't have the sleek quality I tend to like. The finish on the S38II's is very similar, but much smoother and subdued. Who knows, maybe with time the II's will look the same, but I'm hoping not If you want to know how much I disliked the finish on the original S38, I ordered S-series mark II speaker all around for my new setup essentially for the reason that I was hoping the finish on the S38II's was nicer, and I paid just alittle bit more for that hope, too (original S-series are going for a discount right now because of clearouts).
Just my $0.02
The finish on the "black" S38 and S38ii are different. The S38 is a black ash and the S38ii is a black maple vinyl. I prefer the look of the original black ash over the new black maple vinyl. If you're considering the black versions of the S38/S38ii, you might want to go to a Best Buy to see which finish you prefer.