I am dealer for both and have spent a lot of time with both.
The Meitner is a little warmer and sweeter with slightly soft bass. It is extremely musical and if you are supporting your system with a nice powered subwoofer, it is wonderful. I have not tried the new MA3i. I expect the on-board streamer to be a hair more stable. I have had people complain about drop-outs once or twice a day just using JPlay. It is not every hour but once or twice a day is common.
The Linn Selekt DSM with Katalyst is literally what I have attached to my system at the moment. The DAC is not bright and is closer in sound to the Mola Mola Tambaqui. The big thing with Linn is Space Op. The room correction takes this DAC from being in the $10K price range with classic chassis to easily competing with devices that are $5-$10K more. The challenge is it is miserable to setup and you need support from a dealer. The on-board streamer is really good and stable and performs better than you would expect. As an aside, for $2275 more you could get the Selekt with Organik which is obscenely good.
With Linn, if you buy used, it is worth seeking out a dealer who will support you. It provides you support for Space Op and you can get your upgrades through time which can be a big savings long term.
Neither preamp stage is elite. Your not going to replace a $15K preamp with the output stage but both will match preamps that are more modest.