A further option might be a Hornby HM7000 decoder.
pros would be that it's Bluetooth and easy to change the sound profile through the Hornby App , it's a 1A-1.5A decoder so it will drive a single motor LGB loco just fine and Hornby are widely supported in the UK.
Hornby have started to create sound profiles for international locomotives, the first of which is due Q2 2025, for an Italian E656, but Rivarossi also do some US outline steam and of course a Big Boy sound profile in LGB starter set locomotive would likely be epic
Downside would be that you may need to go with a UK sound profile for the short-medium term, compatibility between Hornby and lgb would need to be checked or you could just use the 4A/15V power pack that Hornby provide and plug it straight into the track and set aside the MTS system.
I would add that I've only used the HM7000 decoder in TT so there may be scaleup issues that I haven't seen.