A STATEMENT Next-Gen that is built from the factory is, component-by-component, just the same as an original STATEMENT that had the upgrade treatment. The only real difference to factor in is that an original STATEMENT will retain its chassis, motherboard (with SSD and RAM) and Phoenix output. Virtually all the other changes are all to do with the PSU which is basically a complete and total overhaul.
This does mean that an 'upgraded' STATEMENT to Next-Gen PSU will have differing warranty periods. Example; an original STATEMENT built in 2020 that gets a Next-Gen PSU upgrade in 2026 will only receive new warranty coverage on the new PSU parts fitted - the board, SSD, RAM etc all still originate from 2020.
There is no difference in the processing stage which means the software and feature longevity (or support for Sense updates, in other words) will be just the same between STATEMENT Std and STATEMENT NG.
So to answer a bit more simply, the only real implications between a full unit swap-out via a dealer trade-in, or a return-to-factory upgrade, is basically warranty duration/coverage. Sound quality? Functionality? They're the same.