I think there's a slight misunderstanding here. The SSM2017 is not an opamp but what is called an "instrument amp". A chip like the SSM2015/2017 or the Burr Brown INA 103/163/217 (the latter being a drop in replacement for the SSM2017) is kind of a ready made preamp, there's really not much to be added. If you take a look at the datasheets (Burr Brown available from
www.ti.com) you'll see that you really need only a very few additional parts, no elaborate design necessary. The crucial points perhaps are the input caps (BB suggests bipolar electrolytics but most preamps use regular electrolytics because they're much cheaper) and the output stage which can either use an additional opamp to eleminate the DC offset or again capacitators, again usually regular electrolytics. Or you could get rid of the electrolytics in the signal path by using quality input and/or output transformers. Jensen sells transformers specifically to enhance the performance of SSM2017 and 2015 chips. So in theory there are a few options to chose from, but the less expensive preamps use designs with electrolytics in the signal path. Perhaps the Earthworks uses something better, I don't know, but if they do, that might explain its cleaner sound.
A cheap way to enhance the performance of such designs is to solder a a small (0.1 uF) quality film capacitator in parallel with the electrolytics. Scott Dorsey keeps recommending this on RAP. I've tried this on my Behinger Ultragain 2000 (the old one without a fake tube stage), and it did in fact make it sound more transparent, quite noticably so. It's also a good idea to renew the electrolytics while you're at it. Especially if it's an older unit. Electrolytics tend to degenerate more rapidly if they don't get some voltage. In those preamps only the input capacitators get some decent voltage when blocking phantom power. The output caps are mostly in there for safety reasons and blocking what little DC offset is produced by the preamp. Thus they're prone to decay. Another easy mod is to exchange tantalum capacitators, should there be any on the PCB, for quality film types. Tantalums really cloud the sound. In a chip based design you probably won't find any tantalums, but in a less expensive discrete preamp like the Ultragain 2000 you might. Behringer, for some reason, always used tantalum 0.1 uF capacitators in their older through the hole preamps and processors, even though other caps were film types. After my various recapping experiments my ancient Ultragain 2000 sounds really good and clean, much more transparent than before. I'm sure you can enhance a chip based design that way, too.
BTW: The much rumored 1510 chip is from THAT, not THE. But I wouldn't expect too much by just replacing the 2017. The 2017 is not such a bad chip. The Burr Brown replacement INA217 has slightly better specs, the THAT chip is not available yet, so nobody knows. Some designs use really cheap opamps after the input stage. Those can compromise the performance more than the 2017 itself. There's good reading on RAP about stuff like that, in particular a post by Monte McGuire about modding a Symetrix 202 (you can find stuff like that via Google groups search). But my guess is that recapping and adding those small bypass capacitators in most cases will be the best bang for the buck, it's also the easiest to do. Removing a chip from a PCB is really not that easy, especially if you want to keep both the chip and the PCB intact.
Or just skip the whole modding part and buy a really good discrete preamp. I wouldn't go for another chip based preamp like the SPL, if you want something radically different and better than what you have. Personally, I really don't believe in hybrid designs. Either tube or transistor is fine, but having both in the same unit is like dining with your best friend and a supermodel at the same time.
BTW pt. 2: The last time I checked the INA103 was still available. The INA163 seems to be a slightly simpler version of the 103 at about half its price, but it's only available in SMD versions. The INA103 is through-the-hole.
