To improve image quality at high frame rate (short integration time), you would need to use camera analogue binning and increase analogue gain though I2C interface of IMX219.
Digital gain after analogue to digital converters will only improve appearance, not signal to noise ratio of images.
I’m not sure TX1 ISP is capable of adjusting analogue gain of IMX219. You can use I2C analyser to monitor values written to IMX219 analogue gain register, or add driver debug information from reading IMX219 analogue gain register.