Yeah, I'd consider the Dirac full upgrade to be essential in most cases.
The good news about the XMC-1 (based on what I have read) is that it it's a good unit and it doesn't need to do sample rate conversion for 44 or 48khz signals.
The bad news is that the multi-sub stuff isn't implemented right, so you have to use a single sub output and time align the subs manually.
More bad news is that it only holds a single Dirac preset, so there is no way to instantly A/B test Dirac filters, which is a big shame.
By comparison, the MiniDSP DDRC-88A does handle multiple presets, but it is fixed at 48khz, which might be audible for 44khz sources. Even so, I expect that the Dirac improvements should overwhelm that in most cases.
The PC version of Dirac Live (which I use) supports multiple presets and doesn't need to do any sample rate conversion, but you are limited to using the PC as the only source, so no Atmos or DTS-X.
Gotta compromise somewhere, unless you get a Datasat, which is nuts.
I'd love to see something like a DDRC-88A which does 16 channels at 96khz, with built-in bass mgmt, all for a reasonable price.