Hi, Let's see if we can clear this up. In a PINCH you could use the headphone out (with a 1/4" stereo by 3.5mm adapter) BUT the difference is that headphone out levels and impedance are WRONG... but you won't "hurt" anything (you will suffer quality of audio issues)
. So lets look at the LINE outputs of the Audiobox. When we speak of "line" level there are multiple different types that follow different impedance, and output levels. Lets start at RCA. I'm not going to get into the voltages and impedance (a combined resistance and capacitance) differences, but we will simply say that RCA is a lower voltage, higher impedance (which makes it HARD to send over long distances more than a couple feet typically) CONSUMER gear.
1/4" mono, typically used in musical instrument and pro audio, which has a higher voltage output than the RCA and a lower impedance, which allows it to drive further distances, but still has limitations. Mono 1/4" is considered single ended, (like RCA) but again, when we speak of impedance there are still BIG differences in say a guitar cable (signal) and the line level outs like the ones on the Audiobox (and other Presonus interfaces. Impedance is a VERY important consideration because if you want the sound to be the best possible, these factors have to be taken into consideration, but here we're going to just speak of 1/4" line level. The 1/4" line level outs CAN drive the RCA inputs of a powered speaker, again NOT optimally, but it will work. (Note: 1/4" line level will drive any 1/4" line level input) The difference between the 1/4" mono and 1/4" balanced/stereo is electrical level (balanced/stereo is typically higher and double ended, AND as such the signal is inside a metal shield that keeps the noise level down from spurious RF like florescent fixtures and radio transmitters, and phones.
Balanced/stereo 1/4" line level. again higher voltage (still very small as in around a volt typically) able to drive MUCH longer distances, and are basically the same as balanced XLR, and a cable with 1/4" balanced and XLR on opposite ends of a cable is essentially the same. Typically, 1/4" balanced is tip = hot plus, ring = common/negative and sleeve = shield
So, XLR balanced and 1/4" balanced are essentially the same, capable of long distances because of lower impedance, and higher voltages (again resistance to voltage flow) and the signals are encased to limit exposure to noise...Typically an XLR balanced configuration is pin 1 = shield, pin 2 = Hot or plus, pin 3 = common/negative.
Note here that typically RCA gear is considered consumer level gear.
So, get a pair of cables with 1/4" mono on one end and RCA on the other, note, converters can be used but can be problematic. The better the cable the better the sound (to a point) not necessary to get $50 cables here regardless of what the marketing department says...
