Reference 3a Grand veena or Duntech Sovereign

I've heard both, and think they're both terrific speakers. Note that the Duntechs, while nominally of reasonable sensitivity, really need an amp that can control their woofers, otherwise they can sound a little slow and congested in the bass. I think your amp should work with them, but if there is a way to bring your amp to your friend's and try it with them that would be something I'd highly recommend. The Grand Veenas are probably a bit more transparent and clean-sounding, but in my listening to them I felt they were better with smaller scale ensemble music (jazz, chamber groups, etc.) than with full scale orchestral music. The Duntechs have a much bigger soundstage and overall bigger sound, which suits them for full scale symphonic works. Duntechs probably have better dynamic capabilities in the large scale dynamics; Grand Veena's might be just a little better in smaller scale dynamics due to their transparency, but neither speaker is a slouch there. Both are superbly musical in that they sound like the music you're playing, not an analytical tool. I could live happily with either, but in a room of your size I would probably opt for the Duntechs because I like the house sound, I like large-scale symphonic music and you've got the room for them.

For Wasitpon, since you have the amp and will be getting the Sovereigns, might as well try the combination before making any decisions. They do like a lot of power; my dealer sold a lot of them with Rowland 7 monoblocks, ARC M300s and Krell KMA 200s and KRS, back in the day. The key is having enough control in the bass to handle the woofers, otherwise the sound can get a little muddy and slow.

Wasitpon: I agree with Tbg, 1200 watts from your amps should work fine.

Make sure you're sitting at least 10 feet from them to get the best integration of the drivers.