Pairing my Marantz SR8400 with a power amp. Is it worth it?

Hey there, new to the forum here. I'm in the market for a (likely used) power amplifier to pair with my Marantz SR8400. I'm specifically looking for a stereo amplifier to drive my front two speakers, the Paradigm Studio 100 V3, for music. Having not purchased AV separates before, my big question is: is it worth it on a budget? My budget is between $300-400 so it appears I'll be buying something used (totally fine). I've seen compelling offerings from Adcom, Emotiva, Parasound, and NAD, however, none of them offer a significant increase in power of my current integrated receiver. But does that tell the entire story?
What I'm looking for is a bit warmer sound and increased clarity at louder volumes. The Marantz does well enough, but in a larger room in doesn't quite cut it, and I'd really like to open these speakers up. What I'm NOT looking for is making these speakers any brighter than they already are. The brightness is fine as is, but anything more would be excessive. Any recommendations in my price range? Here's some I've found thus far:
Adcom GFA 5400 (best looking option, but 125wpc)
Adcom GFA 555 (significant power output. I question the quality and worry about the age)
Parasound HCA-1000a (comparable to the GFA 5400?)

Thanks!