Proac 1SC 's are a great fit and not unreasonable used in the market.
There are lots of choices in that price range. First, try running a search on best monitors or best small speaker. One that is hard to find but is really very good is the Sequerra Met 7s. The would probably be about half that price but are very neutral, do nothing wrong speakers that would leave you with the $ to find a good, non-boomy sub, IF you can find a pair. Merlin TSMs are right in that price range, as well.
What is the size of the room and expected loudness level? This will usually dictate efficiency requirement. Cary 300SEI only has 12-15 watts at 8ohms. So figure at least 89-91 dB flat 8-Ohms speakers for a mid-size room for moderate loudness.
Monitor speakers tend to be rather inefficient with a few exceptions. I can think of only Coincident Triumph Extreme and some single driver speakers that into this description.
I did try early EPOS speakers with Cary 300 SEI about 10 years ago. Certainly very romantic sounding but does clip pretty fast. And this was only in my small apartment living room. Just for fun, I did hook up a pair of Thiel 3.6 as well. Surprising good sounding with string quarter and female jazz vocal. Just have to keep the vol down and make sure there is zero bass in the music.
It just goes to show you that SET will work well depending on requirement.
If you don't listen to very loud level, anything with >80 dB will work as long as impedance is relatively flat. So just pick the speakers that you like and make sure it's a flat 4 or 8 Ohms speakers. So the choice is actually quite numerous.
ProAc 1SC, Reference 3A Dulcet, Harbeth, Spendor and etc. Probably smart to stay away from speakers with Dynaudio based driver. Usually too difficult to drive for SET.
For the "magic" vocal reproduction combo, 300B and BBC LS 3/5 speakers is the one to go for. I heard a pair of Cary 300B monoblock with Roger 3/5. Definitely syrupy sweet. Won't be very loud at 82-84 dB efficency though.
I urge you to listen/read, to fullrange, single driver, crossover-less speakers. This is where the "Magic" happenes with the 300B, zero-feedback SET designs. Since you are looking for monitors you can take a look at Omega speakers. They are very efficient as well. Also if you don't mind floorstanders Cain & Cain also fits your bill.
I second a listening of the Harbeths. Their upper range speakers are both bulletproof and a nice listen. If you are considering the Proac's; listen to the Harbeths. I think they're a better speaker for a number of reasons. I would also try a couple of unorthodox things like Joseph Audio's fourth order crossover speaker. Especially the RM7. Or maybe something that might seem wierd like a Martin Logan. Or Green Mountain. In that you already have a crossoverless though (the headphones will be a no crossover design) you may want to consider expanding your horizons, and experiment.