I think if you are happy with your current MA5300 then it seems like auditioning the MCT500 makes the most sense. You didn't mention if you wanted new or used but there's a good chance a McIntosh dealer in your area can probably help get you set up with a unit to try out.
As for upgrading your DA1 to DA2, I personally didn't notice much sound difference between them. The DA2 has some upgrades as far as features and functionality but the sound shouldn't change much if at all. So if you are happy with the DA1 just stick with that.