Dr-100 MK3 signal to noise with external mic

[Bambi]

Hello, I write to ask you a question about the DR-100 MK3 signal to noise ratio. I'd like to know what the difference may be in using the recorder alone or using it together with an external mic. I read in the manual or somewhere else that the recorder gave its best results when a good external mic was connected to it. In any case, what I'd like to know is how would I get the best signal to noise ratio possible, if with or without an external mic. I always use the recorder with the "dual ADC mode" on to get the extra 7 decibels improvement in the sound. My mic is the AKG P420, with a signal to noise ratio of 79 dB-A and a self noise of 15 dB-A. So I'd like to know if, when used together the recorder and the mic, the real signal to noise falls closer to the mic's value, the recorder's value (109 dB), or somewhere in the middle