Speakers for $600.

I'm looking at upgrading my Wharfedale Diamond 9.6s. They just aren't exciting enough nor do they image well enough for me. I'm looking for a used monitor in the $600 price range that would be well suited for jazz and rock. I don't require too much bottom end. The speakers will be powered by an Onix SP3 MKII integrated amplifier. So far I'm looking at the Triangle Stella ESs. These seem to be highly reviewed and meet my requirements. Any reason I should go with something different?
Your ears will let you know, when something different is needed.I bi-amp some paradigm monitors.20,s-v3.very tight sound. bi amped for the best sound .same amp running the high/lows,ok sound.Craigs/list? a pair of kg4s reproduced the best sound, out of many,$150.I,ve a pair of barn finds,Manchester,s?,is the badging.4 speakers, 2 attuns.(junk)Woofer surrounds gone.$50 including, as the guy told me ,speaker cabling, from a lamp.The sound, not to shabby.And i gave the extra cash to my wife(150+50). Good Luck
There is a pair of Spica TC50s for sale on A'gon. Check them out.
live a little. go to the pioneerelectronics.com website and check out the malt whiskey speakers. 600 bucks a pair, lively, balanced, off the charts for a cool collectible at a great price. my brother-in-law, who also owns a set of jvc 'wood driver'speakers, and they sound 'more than fine' on rock and jazz.
I agree with Maddoggy...Klipsch kg4's are outstanding for what you can buy them for (I paid $160 for mine). If you don't mind larger....Klipsch Forte go for around $500 bucks (another outstanding for the money speaker).

Your amp will probably sound great with them!

Quad 12L2s come up under $600 on Audiogon pretty frequently (there were two pair for sale the last time I looked; I don't know the sellers). I have the original 11Ls, which I think are fantastic--fast, detailed, nice imaging, and fun to listen to. I've read numerous similar recommendations of the 12L2s on the forums here.
I second the Spica TC50s, if you understand and can live with their limitations. They don't dig too deep into the bass, they odn't get really loud (although I'd say loud enough), and transient attack may not have the greatest jump factor. But you get supremely evenly balanced tonality across the frequency spectrum, very high resolution, and a natural sense of dynamics within the limits of their volume. One of the most natural sounding speakers ever made, regardless of price. The Angeluses are also excellent. Although I've never heard them, the Spica designer John Bau, felt the TC60s were the best speakers he ever built.
Sequerra Met 7s
My Green Mountain Europas have amazing bass, speed and imaging. Not seem often here but they go for 600 +-
Von Schweikert VR-1 also come to mind
Mobile Fidelity OML-1. Gorgeous and very nice sounding. I agree that the Spica TC-50 are also very nice.