You'll need a digital send/return style mixer, like Pioneer's DJM-TOUR1, DJM-900NXS2, DJM-750MK2 and DJM-450 models. There's a firmware update you'll need to apply to your mixer so it can work with the new app. Once you connect your iPhone or iPad to your mixer via the same lightning/USB cable you use to power your iOS device, the DJ-REC app is ready to go. In addition to recording and streaming, you can edit the time-stamp that's automatically created from the data sent from the mixer to the app, which will let you create track lists more easily. There's a peak limiter, too, to ensure you don't clip out at high volume.
There's a Loudness slider in the app that will increase audio pressure and punch up the bass in those older tracks. If your device isn't connected to a mixer, you can still record with the app in analogue using an external mic. You can play back your mixes via the send/receive USB channel, too, so all those dancers in the club can hear your masterpieces.