Is it safe to connect my Logitech Z5500 speakers to a UPS?

It is not necessary to connect a high wattage speaker system to a UPS. Plugging such a speaker system in a UPS would be a waste of resources. Reason being, a UPS is designed to either give you enough time to shut down your computer, to keep servers running, or to give you enough time to save your game or finish up working on an important document before the battery gives way. Therefore, if you think about it, if the power cuts off and your music is still playing, what sense does that make? Getting those few extra seconds of music is not more important than getting a chance to save your documents before the UPS battery drains. There is no other importance greater than that. Additionally, because the system draws so much power, during a power outage, you'd only get about a minute or two of music before the UPS battery dies, and even less time at higher volumes.