If you want to upgrade for sake of upgrading, there are a lot of options. You can keep your current setup for example and add a DAC/AMP combo for for ease of use. You can consider maybe going balanced, not that it is gonna matter much but it is an upgrade. As far as I can tell, Atom+ is not.
Atom Amp+ is built on the exact same circuit board as Atom Amp. The bulk of the performance boost results from upgrading the input stage ICs from NJM2068 to NJM5532, followed by small tweaks to supporting resistors.