Speaker selector boxes put one more switch between your amp and the speakers. Even when new, that's one more spot to add a bit of resistance to the wire run between the amp and speakers, and time will not help things.
That said, years ago built-in speaker selector switches were standard issue on most amps with few complaints. Whether it is a theoretical issue or one that you can actually hear depends on the quality of your hearing combined with your level of audio nevorsa.
That said, years ago built-in speaker selector switches were standard issue on most amps with few complaints. Whether it is a theoretical issue or one that you can actually hear depends on the quality of your hearing combined with your level of audio nevorsa.