Two thoughts:
1. You have never mentioned that you do any serious post-processing the output of your HDR / fusion process. In my experience, it's rare that the output of HDR programs like Photomatix can be used as is. In my experience, HDR software always seems to need some final post-processing tweaks (like I did on your image) to bring it up to snuff.
2. I don't specialize in interiors, but when I've been asked to do them (and make sure the window view looks good), on of my favorite techniques is the following.
a) Set the camera on a really good, sturdy, REALLY steady tripod.
b) Put a Pocket Wizard (or equivalent transmitter) in the hot shoe for the flash.
c) Attach a small hot-shoe flash to a Pocket Wizard receiver.
d) Attach a remote (wireless or corded) to trigger both the camera (and hence, the flash).
e) Set the flash/ambient exposure balance so that the brightest part of the flash in the scene balances is about a half stop or so below a perfect exposure for that area of the room.
f) Walk around with the flash in one hand, the remote in the other and take 20 or 30 pix with the flash at different places in the room, pointing in different directions (...selecting the best positions for the flash is the only thing that requires some experience).
g) Load all the shots as separate layers in PS with the blend mode of each set to "lighten". Put a no-flash, windows-only shot at the bottom of the stack.
h) Experiment turning the various flash layers on and off to get the best look. Be careful not to turn too many layers on and get an overly flat look.
Once you have done it a couple of times, the above is an amazingly fast process. I've found that it produces very nice results without a lot of thought, a lot of post-processing, etc.. The best part is that it doesn't involve all of the trade-offs that HDR algorithms must make to blend exposures, because it's nothing more than a bunch of ordinary photos, so it can look very realistic, with good, natural shadows. Another nice feature is that you don't have to worry about being in the picture. If you don't want to set up a small light stand and need to be in the picture, just hold the flash such that you are between it and the camera, your dark silhouette will almost always be filled in by the "lighten" mode from one of the other frames, but it's better to avoid this situation if possible.
I'll try to find some pix I've taken this way and post them.
HTH,
Tom M
