I think some basic agreement on terminology will be helpful here. To that end . . .
Line out (LO) is an analog audio signal typically used to feed into an analog amplifier.
SPDIF and the 3.5mm to RCA cord supplied by iBasso are digital out and must be fed into a digital input device. Using this output avoids the D/A converter in the dx200 and depends of the receiving device to perform D/A conversion and analog amplification.
Balanced and unbalanced (single ended) refer strictly to analog outputs and inputs. Unbalanced means that there are 3 wires for the signal path. They are right power, left power, and common ground. Balanced means there are 4 wires for the signal path. They are right power, right ground, left power, left ground. The advantage of balanced is that there are 2 completely separate signal paths that helps to eliminate inter-channel interference. iBasso has said that we should not use the balanced output to drive single ended headphones or amplifiers as this involves shorting right and left ground which apparently causes problems for the output buffers in the balanced circuitry of Amp1 and Amp3. Also, shorting right and left ground eliminates the benefits of balanced, so there is no good reason to do this.
Cheers all