Hi johnmar,
Thanks for that photo. I think that muffled bass I was hearing is due to the lid of the piano being fully closed--even the front hinged portion that is normally closed only when the piano is not being played (to keep dust out). From what I see in the photo, the tail of the piano is backed into the corner of the room leaving little room to either side of the piano case. That can be a very important consideration if you play classical music, as the mics in that case are more often than not set in A-B configuration in front of the curve of the case anywhere from 4 to 8 feet away in order to capture finished, blended sound from sound that has totally exited the piano, which is preferred for classical.
The limitation above would not be so important for jazz, pops, and New Age which more often use close-in recording techniques. For close-in the mics are often set up to capture the percussive noise of the hammers striking the strings. For example, the mics might be placed on stands in XY configuration (with the two mic capsules virtually touching at a 90 degree angle) within 3 feet of the curve, directly next to the case rim, or even inside the piano using ribbon mics for example. Close-in recording makes mechanical sounds more apparent. It is not yet finished/blended sound, but instead sound in the making that has not fully left the piano. But pianists doing jazz and pops often like that.
You posted both a classical piece and a New Age, so I'm not certain if you generally play one genre more than the other or if it's an equal mix.
In putting the mic's in a T configuration as shown in the photo, but having the treble mic pointed closer to that wall than the bass mic is to its wall, is the idea to catch the reverb off the reflective wall surfaces being biased to the treble? Or capturing what rises through the closed lid? Or both?
Here is something that some other pianists here have done, sometime very successfullly. You should try it at least once. I believe your TASCAM has built-in on-board mics. As an experiment, disconnect your AKG mics from the XLR jacks. Place the recorder on top of the closed lid behind the long hinge that separates the two parts of the lid, and center it such that it is parallel to to the hinge and aligned with you sitting on your bench. If in the manual you have a choice of using the cartioids only, play the first few bars of the Chopin with that (just the excerpt is sufficient). If you can then do it with the omnis, record the exact same bars using those. Or if you must have both types on at the same time, then just record the same excerpt with that. Your out take right now is a bit loud! You can simply turn the input volume nob down slightly. (When you get a recording and transfer the file to your PC, it should sound at your intended volume when you have your PC speakers volume set on 12:00 noon position. Most listeners will experience it the same way with their speakers. That way you won't blast off the headsets of people listening.
That adjustment will take a little tweaking, but once you get it right, just leave it alone. So just for kicks try this test, and let's see how it sounds.
Once you've done that test, that will give you a direct comparison with your external mic placements versus the on-board mics sound.
Two more ideas: If your C3 has not only a full lid prop, but also a shorter "singer stick", you could open the lid only that high on the singer stick. (I understand your reluctance to use the full prop due to reverb from that right wall.) If the singer prop is still too much, try this second option:
Have the lid closed but open the front hinged portion of the lid and fold it back. Then using your T-configuration for the external mics, place it on top of the folded back part of the lid, but centered between bass and treble. Play your excerpt and see how it sounds. The sound should be richer.
There might be some other options down the road of using two mic stands at a 5 foot height down by the tail of the piano, although it'll be a squeeze. With the freedom of having two mic stands, you could also try placing the two mics in A-B configuration parallel to one another with 12 inches separation set and centered in back of you where the room is more open and about 6 feet behind you as you play. But at the moment you don't have stands, so that might be something for the future.
I hope this at least gives you some testing ideas. As I said, it all comes down to experimentation.
Other readers here might have additional thoughts on this too.
David
Topic: my new recording rig has arrived