"to be heard above the music" – above what music? If it's some fully-mastered mixdown that you're replaying at 0dB, then this is no surprise: such a track has lots and lots of compression on it, making it way louder than a clean microphone track can ever possibly be. You may feel that it's the microphone that's too quiet, but in fact "everything else is too loud". What you can do about that – well, turn up the headphones level, make the backing track quieter from the software side (something like -12 dB), correctly set the preamp gain to just-not-clipping, and start recording. That should work out fine.
Note that, for many musical styles, clean solid-state preamps aren't really great for the vocal tracks anyway. Have you ever tried a tube preamp? That allows you to set the gain quite a bit over the limit, resulting in a powerful, driven, yet still warm and pleasant vocal sound. This is also quite helpful to have on the recording headphones, as it gives a very direct, clear and still dynamic feedback to the singer. I also like to put a subtle analogue compressor (something like ratio 2.5:1, threshold -10 dB, soft knee, attack 10 ms, release 150 ms, gain +2 dB) right in the recording chain sometimes. All of this will make the signal a bit louder, without ADC clipping.
But you shouldn't do anything more powerful than this: the downside of all such measures is that you won't be able to alter the effect afterwards, like when you find the vocals should after all have a bit more "open" sound. No hard overdrive or brickwall limiting, please! It really shouldn't be necessary when you don't use too loud backing tracks.
Of course, it's possible that your interface's preamp is simply broken. If the signal is even quieter than a backing track at perhaps -18 dB, then something is wrong. You should check this with your DAW like suggested by Lukas Woltjer.