Probably too late now, but the main differences are:
S2 - weaker headphone amp, MQA/Roon support, remote included, smaller
DX7S - stronger headphone amp, higher output impedance, balanced HP out, XLR out, AES input
So really you'd have to decide what features matter to you since they're similar in price. Personally, I think you're getting more with the DX7S. If you don't care about XLR out, the Topping DX3 Pro might fit the bill for you for...