I think you need to take a step back and consider what you are trying to do.
This thread was about suitability of an audio ADC for instrumentation use. The main problems mentioned are calibrating the gain and the frequency response. At present, the gain has been guessed but not checked, and frequency response remains unknown. It is also not clear what software you plan to use for analysis of your recordings and what it needs for calibration of gain.
There has been a lot of discussion about noise, but you don't seem to know what signal-to-noise ratio you need for your analysis. You have been trying to track down noise which appears in measurements of a simulator, but the amount and type of noise generated by the simulator is unknown, meaning that it may or may not be representative of real data. The noise hunt has been made more difficult because the noise measurements may be inaccurate as the gain of your measurement system is not calibrated.
I would suggest taking some time to calculate where your major noise sources are, and how they impact your signal-to-noise ratio, and in turn how they affect your analysis.
The formula for thermal noise in a resistor is easily found with google, and a writeup is found at
https://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise#Noise_voltage_and_power.
If you want to reanalyse your amplifier to see what changing various components makes then, I think main noise sources in the signal path are:
Source resistance (e.g. 10 kOhm)
2x 5k protection resistors
2x op amps (20 nV/sqrt Hz for the original LF412)
Instrumentation amp (5 nV/sqrt Hz for the AMP01).
You are interested in a bandwidth of 1 kHz:
So the calculation becomes:
10k Source resistance: 0.13 * Sqrt (10000) * Sqrt (BW) = 411 nV rms
2x 5k Protection resistors: Sqrt(2) * 0.13 * Sqrt (5000) * Sqrt (BW) = 411 nV rms
2x OP amps: Sqrt(2) * 20 * Sqrt (BW) = 894 nV rms
I amp: 5 * Sqrt (BW) = 158 nV rms
The noise powers sum:
Total = Sqrt (411 ^2 + 411 ^2 + 894 ^2 + 158 ^2) = 1078 nV rms