Ah, I see you posted an attachment while I was righting my first response... Besides I had to pass out candy at the door - unwillingly as I am a dentist by profession, and music is a hobby.
OK, I just listened to the piece. I am hearing the room nodes on the same frequencies that I had calculated in my first response. Based on your room dimensions they should occur at 70Hz, 80Hz, and 125Hz. I've never played this piece, but sounds like it's in E Major and the pedal notes, low E and B are 82Hz and 123Hz respectively - very close to the calculated nodes for that room! To improve the sound and treat the room, the recommendations I outlined before may be a good start.
I also realize in your follow up post that it's an upright. So, you can't mike it the same way you would a grand. Try placing the mics 3-5ft on back of the piano OR Open the lid and place 1-3ft from the top OR Open the bottom lid and mic 3-5ft away to start.
Yes! With the SP B1 mics, you can definitely improve upon the sound even though they may be on the bright side, but they're still transparent and that's a requirement for piano recording. There is a good deal of noise, most likely from the audio interface. Make sure you check input settings, mic cable, phantom power, impedence settings, gain, and power supply for any anomalies on the interface.
If you can't improve the sound from the current audio interface, try a Presonus or MOTU interface if you're intent on a computer based recording system. The threshold for good quality starts at $300. Most interfaces skimp on the analog inputs, and that's where the money is in the "sound" or "color."
BTW - If you're planning on a holiday gift, get the M-Audio Microtrack II recorder - has very good A/D converters, built in full 48V phantom power, and extreme portability - all in a self contained handheld unit for $300. You can use your current mics to it's full potential. I use one, and it's the best value IMHO.