The path I’ve always taken was as I upgrade my source gear (DAC/amp) I find that I also eventually upgrade my headphones, and vice versa. The HD650 is a classic and it has it’s qualities that many people love but if you’re looking for the biggest upgrade for your tastes then the headphone would be the first thing to consider. Going down the rabbit hole of compensating for a headphone can be tedious and expensive. Have you heard any other headphone with the Mojo? If so, how did you like the pairing? It looks like a wide range of options you’ve got there. I haven’t heard the Z1R but many report big bass from them and a bit V shaped signature. I haven’t heard the AFO but I love the ETHER Flow open and others I trust have said they don’t sound too different (Rob Watts loves AFC with Mojo by the way). I have the LCD-2.2 (2013) but it’s no longer used much as I find the ETHER Flow a much better headphone. I LOVE the Utopia because it has a lot of dynamic punch but it is very forward (I don’t find mine bright though). I haven’t heard or read anything about the Aeolus. I can’t stand the brightness of the HD800S. But those are my opinions so they’re not really going to apply to your tastes.