Consideration of amp change

Been thinking about a possible change of my integrated amp (current Classe CAP 151) and have under consideration the ARC DSi200 and or Sim Audio 600i. The front end is ARC CD 3 Mk 2 with Apogee Slant 6 speakers. I listen to rock, soft rock, jazz, new age and blues. I'm hoping to expand the sound staging (without being analitical) and want to try to expand the micro details from the music I listen to (see my system for all the details). My biggest draw back is that I don't have access to hear these pieces of equipment for comparisons though so I have to rely on educated opinions. I DO NOT WANT to go separates, (so please don't suggest any of that). Suggestions are welcome and appreciated and I'm working with in budget limitations with a top of $3K-$3.5K
There is a almost new Modwright KWI-200 integrated at 200 watts /per channel that would have the sound you're looking for at just over $3000.  I have had 3 Modwright cd/sacd players and loved them all.  Dan at MW stands behind his products incredibly well.  
top-end of your budget stretch for a used model but a punching heavy Goliath killer.....

REGA OSIRIS...Google the reviews.

highly recommended
I heard the Sim Audio and it was fantastic. It was setup with Dynaudio Confidence 1 Platinum speakers. It may have been the 700 though. I'm not sure.
I would recommend the LSA Statement Plus integrated amp currently for sale on Audiogon.
The Modwright KWI-200 is also a good recommendation, or a BAT VK-300SE.
Many good integrated amps out there these days.
The Sim is a good suggestion, but I see that there's a Coda CSi for sale at 3k (possibly negotiable), and knowing how well it drove a pair of Maggie 3.6s in a friend's rig, it would probably take to those Slants really well.
And this!
I had a pair of Apogee Centaurs which I think the Slant 6's would be similar to. I'd second the ModWright. At the time the best sound I got out of my Apogees was with a ARC 100.2 over some Levinsons and Krell's I tried at the time which were too analytical on those speakers. The 100.2 is a great amp but not sure if the DSi200 has the magic the 100.2 has. Personally the newer ARC SS amps don't do it for me. Between that ARC and the ModWright on your speakers I'd go with the ModWright if you can't hear them first.
I never felt my Centaurs were that hard to drive like the big ribbon Apogees; the Slant 6's should be the same. I'd read up on a Rogue or other tube integrated pieces. When I was using my ARC 100.2 on my Centaurs I was using a MidWright SWL 9.0 SE preamp which worked great on the Centaurs. Unless you flat out don't want to mess with tubes I'd look there as well. 
Meant ModWrigt... not MidWright
Wish one could edit their text after posting. Old eyes and fat fingers on an iPhone. Third time on spelling - ModWright.
Another vote for ModWright... great company and outstanding products.
Modwright....Dan is great to work with! 
You should check out the Octave MRE 220 mono's.  Unbelieveable!!!
I'm an extremely happy owner of a Sim Audio 600i. I bought it to replace an AR tube separates setup as my family couldn't deal with a non-automated system. I listen to a wide gamut of music: Zep, Rosanne Cash, Talking Heads, Beethoven symphonic and Beethoven piano, Diana Krall and Serge Gainsbourg, for example. I should point out that my speakers have a titanium inverted dome tweeter and a ceramic driver so they're not necessarily the most mellow thing out there. No worries. The 600i is superb with them. (I've never heard your particular speaker. My first high-end speakers were a set of Apogee Stages but that was long ago and I can only remember their transparency. I used them with the AR tube setup.) Micro detail is everything you could ever want without being fatiguing. The amp is musical across the spectrum with bass being tight and powerful, though never overly so, and even the deepest bass notes discernable as different in pitch from each other. Mids are open with beautiful timbre and highs are clean but never shrill. The soundstage is good but not mindblowing as I would not call this a "forward" amp; it's a "middle" amp. I'd say the only time I miss my tube setup is in the weight or three-dimensionality they give strings in chamber music or when someone is plucking an acoustical guitar that is well-miked. Nonetheless, this amp has better pace than the tube setup - I often find tubes slow. That being said, I think the 600i is about 5K used which is more than you're planning to spend. I considered the Osiris (recommended by someone upstream) but never did audition one. I happened upon the used 600i while I was auditioning a Hegel H360 (which I hated) and it was pretty much love at first note.  ModWright was also in the running though I didn't get around to auditioning it either but they're well reviewed and I like the idea of a smaller manufacturer. I'll just throw this in - and as you know there's a ton of stuff out there - but Wyred4Sound integrated are supposed to be category killers and they do offer a home trial program.  Good luck.