No ADF = No IFR within UK CAS
This is much less of a problem now, as the after market add on kit for the Cirrus is becoming well understood.
If you want to have ADF DME in your cirrus its now quite easy. The King DME is a remote unit that slaves off the Garmin VOR/LOC/ILS frequencies and auto tunes to the DME.
It then reliably displays the DME on a little panel annunciator.
If you want the ADF if can be fitted in the "bolster" in the P2 side of the aircraft and displayed either on the PFD or on the "spare" engine guage (blank socket)
I think DME is good stuff, as it can be clearer than the multiple waypoint distances displayed by the rest of the kit - less possibility for confusion in cockpit (maybe). The ADF however is pointless, most airways flying today would never use an ADF for en-route navigation, and for approaches, they are very inaccurate as everyone knows!
But you can get it all for a Cirrus of you like this stuff.....
I personally make a point of never flying NDB approaches in real IMC. I like precision......