Which speakers are ideal to pair with a Yamaha as3200

You could easily make do with that room..Simply moving that white chair away from the front left speaker,then putting the speakers on appropriate stands(they don't have to be expensive or fancy,just sturdy & solid) pulled out even 18" would help immensely...

Honestly, you may consider pulling your LS50's in and certainly away from the chair.  If you want to get the most out of what you have, setup a unilateral triangle.  This will at least get you started with getting the best out of the LS50's and giving you a better idea of what you're looking for in an upgrade. 

Sorry but the white chair is not always there! Is my  error doing the photo!

But using isoacoustic is not good? Using stand is so much better?

The IsoAcoustics are good but it’s about 3 things..Getting the speakers elevated to where the tweeters are more aligned with the ears..Getting the speakers pulled out from the back wall enough to allow the soundstage to develop & getting the one speaker off that subwoofer..Even the IsoAcoustic isn’t going to alleviate the damage done to the sound of the speakers by the deep bass being transfered to the speakers driver & cabinet...
 You might also try pulling the center speaker out to the front edge of the cabinet, angling the center speaker up towards your ears as opposed to firing straight ahead at such a low listening height & using some kind of isolation between it & the stand/rack...

If you like open baffle  the callidan  

Or new sonus Faber G2 -5 

For $6k tons of trickle down technologies