How much does this noise differ between different daps with balanced outputs 2.5mm? Is it inerrant or is this a flaw of the n5? I'm looking for a dap preferably with both 3.5 and 2.5 balanced out, within 350 usd preferably, are there any negative consequences to a dap which has both of these outs? If you have cans with a special balanced cable, and you want to plug into a 10 buck fiio converter to 3.5mm do you lose the investment of the cable SQ? Are the 30-40 usd converters or the 179 usd by AOL worth it?
If you want 2.5mmm balanced connection without any real balanced amplification to the least, then the 2.5mm and 3.5mm should have the same level of background noise, the 2.5mm might have slightly (I really mean slightly) advantages because of extra ground connection, but the same connector will also mean smaller contact area on the L and R signal pin.
If you want balanced amplification or fully balanced design, then you'll involve more components because you need four channels of signal (L+, L-, R+, R-) processed and amplified independently while in non-balanced output, you only involved 4 channels (L and R). This will inevitably increased the cost of the product. The noise problem won't be as obvious if you are using desktop products as you can have ample space for the circuit layout, but to clamp twice amount of analogue components (starting from two DAC chpis in many cases) into limited space of a DAP, the interference will definitely be more serious then the non-balanced DAP, there are tricks we can do to lowered the interference such as adding filters, lowered the output, reduce the operation current etc etc, but most of these tricks will affect the sound quality as well, so if we are going for a budgeted DAP, the balanced circuit does not necessary improve the sound. If you compare a non-balanced DAP vs a balanced DAP at US$350 budget, I don't think the balanced circuit will generate any obvious audio advantages.
Last but not least, please do not compare the 3.5mm output and 2.5mm output of a balanced amplified DAP and use that as a judgement of the two format. You are comparing 50% of a DAP against 100% of a DAP, this is not a fair comparison to start with.
Regarding whether you can hear the background noise, it relates to specification of the IEM (both impedance and sensitivity), the music you are using (whether it has quiet passage in between), and most important: whether you are sensitive to noise or whether you are "looking for it". So tell use what IEMs you are or might be using and your type of music, we can comment with more confident when we know more details.
