Re: Are my expectations for Sierra-1 to Sierra-2ex upgrade out of touch with reality?
So, I've been through all four possible iterations of the Sierra bookshelves. I first bought S1s in like 2010, shortly thereafter upgraded them to S1 NrTs, then not that long ago upgraded those to S2s, which of course caused Dave to almost immediately release the S2-EXs, and I went ahead and did that upgrade, too. I guess I'm a serial upgrader.
The S1 is a terrific speaker in its price range, but it does have its limitations. As is not uncommon in fabric domes, there's a little lack of sizzle in the top end. Bass extension is very good for a bookshelf speaker with a 5.25" driver, but there's only so much you can do there. Still, an engineering marvel, particularly for the price. Maybe a smidge on the laid-back side.
The S1 NrT is the solution to the S1's lack of sizzle. Amazingly crisp highs for a fabric dome, with the added benefit of some additional clarity in the upper mids. The resultant speaker is also more forward than the stock S1. Because of that, the S1 to NrT upgrade is maybe not for everyone. It was right for me, but I wouldn't universally recommend it universally unless what you specifically want is that top-end sizzle.
The S2 is a pretty different animal than either of the S1s. A detail-recovery monster with tremendous wide soundstage and superior imaging. Brilliant treble. Splits the not-all-that-big difference between the S1 and the NrT in terms of laid back vs. forward, just a terrifically neutral speaker. Bass clarity improved vs. S1 models at the cost of a smidge of bass extension. A hard speaker to fault... until you meet its sibling.
The S2-EX is another engineering marvel, absolutely worth the relatively minor price difference over the S2. Frankly, IMO nobody should buy an S2 or upgrade to an S2, just go straight for the S2-EX. It's not that there's anything wrong with the S2, it's just that the EX is just straight-up better everywhere that the two are different. No change in character vs the S2, no loss of those gorgeous highs, but more bass extension than not only the stock S2, but over the S1. Even better bass clarity, too. Frankly, the bass on these is kind of brain-melting for a bookshelf speaker. They really do go sub-40Hz; they sound like towers. I was hoping to get rid of the subwoofer in my setup and they let me do it. (And I'm a bass player, so my standard in that range is not trivial to meet.) As a bonus, better midrange clarity, too, but not as dramatic as the difference in bass performance. It's the S2 just turned up to 11. Even looks better with the grilles off. That this speaker can be purchased for well south of $2K is slightly crazy. Dave is basically giving them away. (Now, from what I've read the Burchardt S400 gives the S2-EX a run for the money on the quality front, so maybe that's why Dave keeps the EX price where it is so he can undercut the Burchardt. I don't know, I've not actually heard the S400s, but they do measure well.)
So, while the S1 is a terrific speaker (especially for the price), the S2-EX is pretty much better than the S1 at everything. Highs that are both crisper, smoother, and more detailed? Yes. More full-bodied and clearer mids? Yes. Better definition and extension on the bass? In spades. If you think the S1 is close to where you want to be on bass performance, just wait until you hear the EXs. Night and day. It's more than a grand to upgrade a pair, so it's not cheap to do this, but there is a reason for the expense.
Oh, and you're right, your definition of "warm" is not typical. "Warm" usually means a frequency response bump in the lower mids/upper bass range. As far as I'm concerned, terms like warm/bright/dark/V-shaped are references to flaws; places where the frequency response of the speaker is not flat. So asking for added warmth to a neutral speaker just makes my head hurt. But I get what you mean.
Luna Duo V2 LR, Titan Horizon V2, and Rythmik L22 & L12 in HT, Sierra-LXs in study, S-2EXs and Duo V2 C in bedroom, S-1 NrTs in dining room, S-1s at work, HTM-200s in kitchen. Brother owns CMT-340s and dad has a pair of CBM-170s.