Hello John! if you have an iPad you can use a small adaptor that allows you to charge the iPad while sending audio out through the small 1/8" stereo headphone jack. The one that I have is "Model CAAB" purchased on Amazon I think. This is USB-c format but lightning versions should be available if that's your iPad's format.

In addition to above: FWIW ..... I agree with others here ..... I'm no BIAB expert but I have been a performing musician for a few decades & used MP3 backing tracks through several different PA systems extensively. I highly recommend against using MP3 format for backing tracks here's why: Imagine you have a cheep low resolution digital camera and you want to blow up your photos, the results are blurry and hard on the eyes of the viewer. if you are close to the picture you may not even be able to decipher the image at all. Now apply that concept to amplified audio files. The additional cost of the storage required for larger files is worth the results in terms of sound quality and listener experience.

Maybe the better quality backing tracks won't get you paid more and Mp3's will get the job done "well enough" but in my opinion: Being AWESOME is way more fun than being adequate.

MacBook Pro M3 Max Sonoma 14.1.2, BIAB Audiophile Edition 2023, Logic ProX 10.8.1, Focusrite 8PreX Interface.