Kusina, Your room is very similar to mine in layout (though different dimensions). The large opening can be very well tamed by toeing in your speakers. You are probably a bit heavy on the walled side vs. the open side, due to the reflections. Toeing in your speakers will help to alleviate some of the added emphasis to this side of the room. My experience is that the balance control will help even out the sound, but my experience is that it has a negative impact in terms of sound staging. If you are going to address this with a preamp with balance controls, the Capri would be a good unit as would their top of the line model (which may be better budgeted to your system). The suggestion of a TACT preamp would also be interesting, while I have not personally had such a preamp in my system, they are supposed to be capable of addressing such issues very well. The overall sound and all that digital manipulation is what concerned me with the Tact units - but others report very favorably about their performance.
For what it is worth, my walled side (which is all windows) I address the problem with heavy curtains that I close for critical listening. This has balanced it out nicely and I don't find my balance being out of whack, so to speak. I also have my speakers toed in and sit closer than you to reduce the room interaction.
For what it is worth, my walled side (which is all windows) I address the problem with heavy curtains that I close for critical listening. This has balanced it out nicely and I don't find my balance being out of whack, so to speak. I also have my speakers toed in and sit closer than you to reduce the room interaction.