Here is my professional and personal experience in doing what you are doing...
1.) You should first look at linking the digital modes at a network level. No RF linking should be used at all such as in the case of a 'spot' device transcoding. To many problems and to many errors can occur mainly because 'spot' devices are tunnels (bad data in -> bad data out).
If done at the network level then things will be much better and the bad BER's will stop at that modes layer.
2.) The analog audio is going to be your stickler here and more so analog -> digital and not digital -> analog. I have made it sound like the digital -> analog is like using a broadcast microphone on FM. Meaning BOLD, CRISP and CLEAN except when bad or weak RF digital signal comes into the system. You might need to deploy an audio mixer to pull the lows up and the highs down. Also the weak signal FM is going to sound like crap without a doubt. Depending on the system and set-up you might even need to do a squelch hysterisis on the FM side of things.
3.) Plan your DMR feed and from what networks into the system. I am not sure where your TG is housed or stored but the network is going to be a BIG factor especially if pulling over the traffic via MMDVM.
4.) While the controller idea is good do not do that method as you will be doing a double vocoding if going from a DMR radio to a Fusion radio. The audio will sound bad and will be problematic for sure.
5.) EDUCATE - EDUCATE - EDUCATE!!! The users need to know that this is a cross-patch/link and that it will sound different. I persoanlly have heard a person on the system one day saying it is great and good and the likes, then turn around the next day and complain that it sounds horrible because someone had bad audio. Part of the reasons is that audio level setting will need to occur and take place. I know I will get flamed for this but pass on by the cheap chinese DMR radios or DMR radios that do not have an audio adjustment at all. This will cause an audio ripple effect.
6.) Finally, understand that EVERY single radio user, per mode, per make/model, will be a resident expert and tell you that it sounds like crap or is horrible. Yet have them listen in a blind test and they cannot tell you the difference between modes at all.
Good luck and please report back on your progress.
