I like the 197s very much (despite their flaws), as I like the way they look, and the way they sound with their "172-style" engine/gearbox setup of MTU 1800 Series and 6-speed ZF, going up and down the gears (indeed, and I'm not sure if anyone else realises this, but when the 77th 197 enters service, it will also be the 200th 6-speed ZF Diesel Multiple Unit - 172/195/196/197 - to enter service in Britain).
I am however intrigued - what it is that you think makes the ambience in a 197 far superior to that in a 158? The air conditioning obviously works better, but what else? Just everything being newer / less used (even compared to a refurbished "Welsh" 158) or what?
I believe the latest estimate from Transport for Wales is that the ETCS-fitted 197s will enter service on the Cambrian in January to March 2026 at the earliest.