The Enspire is all about high definition midi – that's how it records and that's how it plays best.
It does not make .wav files – only XP (high definition) midis can be recorded by you into its database. Among the 500 or more proprietary tunes loaded into your piano by Yamaha before purchase, some have audio accompaniments in .wav format. These are controlled via the iPad that comes with the piano.
Yamaha's .wav files only contain the accompaniment tracks which play thru the speakers of your piano. These are automatically synchronised to play with separate midi information which drives the solenoids of the hammers and pedals of your piano. On older models of Disklavier, I understand that midi info on USB gets automatically synchronised to play back with CDs in the tray of the 850 controller.
You will never get the type of audio file you want directly out of the Enspire. If you want to capture the full realistic sound of your piano, you will have to make recordings using a microphone.
But what about MusiCast? you ask: To hear your piano playing through the piano speakers or a MusiCast system, your iPad controller must be used to switch on an inbuilt player (in the Enspire hard drive unit) which then uses quality in-built Yamaha sound fonts to artificially re-create the piano sound with pedalling, putting it out through both the piano speakers and the MusiCast system. ;But it is only an approximation of the fabulous quality of sound that your piano can give from playing it live.
If a Yamaha .wav file is playing the piano and it has an accompaniment, that accompaniment will be heard coming out of the piano's speakers, but there is a separate midi track linked to that audio track, and that is being read by the drive unit in your piano to move the solenoids. Switching to Silent Play will divert the midi signal to the inbuilt player, where sound fonts will convert the signal to an audio track which then goes out through both the piano speakers and the MusiCast system.
I guess that the audio signal coming from the Audio-Out RCAs could be tapped and sent to a microphone input, but that is little better than what I have been doing with midis and sound fonts and conversion to .wav from inside my computer.
I intend to buy a microphone for much the same reasons as you, although, for the moment my smart phone and video camera seem to make sound recordings adequate enough for my present needs.
If you tell me of some of your favourite composers, I will send you some superbly played files to put thru your Enspire.