Hmmm...seems like he's asked a pretty straightforward question and has said he's already checked the archives for answers so I'll give him the benefit of doubt (and yes, this topic comes up ad nauseum, but I do understand the OP is looking for some current specific experience).
I've had 3 different pairs of Silverline 17's but not the 17.5's so I'm not sure how valid my input on the 17's are here, but FWIW - I did not find them (SR17's) as efficient as claimed, at least not to the point that I particularly enjoyed using them with low-watt amps (and I tried a few, and they do sound great with tubes BTW...alas). I do like those speakers a lot (or why would I have owned three different pairs over the years). I'm not certain that I agree that tube watts are any more or less than the equivalent SS watts. The two topologies handle distortion differently and thus may make it occur that way, but watts is watts as far as I understand (which may not be very well). That said, I could only get satisfaction with a minimum of around 35 watts with the SR17's I owned. Less power that that consistently left me wanting, and in one case (see Aleph below) slightly more power also left me feeling flat. Though they sounded just wonderful with my 8 watt SET amps, they could not be pushed to any kind of realistic volume without distortion.
As far as SS amps that sound like tubes...a major trend in criticism and marketing, along with tube amps that have SS balls, and other variations on grass-is-greener siren calls...I won't bend your ear with even or odd order distortions, but I can make a few general suggestions that float my boat (I like good tube amps as well) that might make nice music with SR17.5's. If he pushes his limit$ just a bit I'd suggest a (used) Ayre VX5e or Modwright KWA100se or KWA150 (not sure disclaimer is necessary since I'm pointing to the used market, but: Dan is a client). There was a recent thread that included these amps that I contributed too, but too lazy to look it up right now. I might have also suggested a Pass Aleph, but I did try an Aleph 5 with the SR17's and it really left me flat with that amp, which surprised me. No experience with First Watt to convey. You did not mention which preamp he'd be using and that would make a difference on how any amp would perform.
Hope that helps...