All I can offer as I had never seen that logo - Duh! - is that most have been there since the park opened (you get to know them as old friends). It's probably unlikely that 21 year old speakers would still be in production but you never know. I'd always presumed that the speakers were the standard ones used in the US parks (Soundscape?). Looking on various sites and reading reviews, it seems that the 51 has been in production for around 10 years (at least the comments like "I've had these for seven years now" don't date back before around the 2004 mark). It's quite possible that around that time DLRP upgraded some of their dud speakers (DLRP speakers are very unreliable with many being poor quality/volume or just plain not working!). They may well have a contract with Bose as, reading around, they seem to use Bose a lot for their various speakers - including for the parades.
An email to DLRP may work. They are (or, at least, were) very helpful over things like this.
