I primarily watch movies.
I currently have Definitive Technology speakers
8060st’s (Floors)
8060cs (Center)
8080SR (Sourround)
if you were to replace for something different. What would it be and why?
if I were to switch to Klipsch would that be a downgrade?
A lot of folk (who like Klipsch) love the sound, but many of their Speakers are not very accurate in terms of Sound Reproduction. On the other hand, many comment that the resulting sense of immediacy (speaker characteristic, dynamics, perhaps? or coloration due to their voicing?) is very powerful.
Since you asked, I would consider Klipsch to not be an upgrade.
(I'm also not a DefTech fan, but I have no experience with yours.)
Depending on your budget and aesthetics, keep your eyes open for JBL. The Studio 5s are still alive and likely to go on deep sale again, soon. The Studio 6 Speakers will be coming to the US soon, and these look to have good potential. Then there is the JBL Synthesis HDI Speakers.
Since Center channels are so important in HT, solving for that could be the key to a good upgrade, too. Looking for a good 3-way center with Tweeter-Mid in between the woofers is important. Or, resetting your system to allow for a vertical center channel. Or something with a coaxial driver that is doing Highs and mids like KEF.
Your budget and what you are willing to do for set up is going to be key.
Also, you should consider an upgrade at Sub if you don't have one.