Maybe this was already mentioned here in the past; anyway, I think it's important to be mentioned for those who are considering to get PSR-SX700.
We have two options to record audio music that we're playing from the keyboard. First, most used option I guess, is directly into keyboard user memory (or onto USB stick). The process is simple enough and explained in keyboard's manual. However, what isn't that obvious in manual is, how loud will music be recorded. To keep it short: the loudness of recorded music can be set in Mixer->Master tab->Compressor: Output knob. By default Output knob is set to 62, and this value will also be used of we turn compressor to Off.
Why is that important... because it means, if we set Compressor On and change Output value, then that loudness will be used for recording regardless of Master Volume knob position on keyboard panel. Means, we can quiet listen to what we're playing, however recorded song will still have the level (loudness) as set in Compressor-Output. I'm sure you realize how important and welcome that feature is.
Now the reason for my writing... For whatever reason, it might/will happen, that we need to connect the keyboard on external audio mixer or on USB audio interface. And the only way we can do that, is by using Main Output jacks on back panel. The problem is, these two jacks are influenced by Compressor settings and by Master Volume knob on main panel -and we have no option to prevent that. Ok, but where's the problem actually? I'm glad you asked... The problem is, if you wish to record your (live) performance, it will be hard (or even impossible) to find a compromise between desired loudness for your audience (or your headphones) and at the same time, to have desired loudness for recording.
Or another scenario: you wish to use condenser microphone for (Youtube) video you're making on late evening. Obviously you don't wish to make a party scene at late hour, so you will keep keyboard loudness more on a quiet side. But at the same time, you wish audience to enjoy your music (loudness) in full glory. Yes, you can use headphones (which doesn't look that good on video), but the problem remains the same: you're forced to listen the music loud (=loud enough). Another solution comes to mind: set keyboard quiet enough and increase gain on mixer... That doesn't always work, because most mixers don't have enough gain. And in case of USB audio interface, there's usually no loudness/gain control at all for line inputs.
My thoughts... If all above is important for you, then you should consider PSR-SX900, which also has Aux outputs. In manual it's said, that Aux output isn't influenced by Master Volume knob. So, even if it's not mentioned, I assume it is influenced by Compressor Output setting. If that's true (should be confirmed by someone who has SX900), then Aux output behaves the same way as in case of onboard audio recording -which is what we want. Beside that, Aux output on SX900 also have some other features/settings that you might find useful.
Of course we can do audio recording from Main Outputs on SX700. It's just not that comfortable and usually requires more work (post-processing) afterwards.
I hope I provided some valuable info,
Bogdan