$400 is a reasonably good price for those speakers, IMHO. I personally own a pair of those that, unfortunately, are in storage since I moved. I originally had SDA 1C's but with I came across the SRS II's for $200, well, enuff said. I've updated the crossovers in mine with Solen caps and Mills resistors plus changed out the tweeters to the RD0-194's. Yes, they really, really like whatever power you can run on them. When they are going, they run off of a Carver TFM-55 amp @ 380wpc. Before that one, they were on a 200wpc Carver M-1.0t plus I've used them on my 250wpc Soundcraftsmen A5002. You don't "have to" give them that much but don't even waste your time running them on a smallish vintage receiver. That would just not be right!!! Also make sure it is a common ground amp as these speakers have the IC cable between them, too. After that, it's all about the proper location and listening position then let them rip!
Enjoy them in their stock form, though, first. The "upgrades" don't have to be done. Let your ears decide that. If you like them the way they are, go with it.
Also, there are 2 iterations of the SRS II's. One version used the pin/pin connector and the other used the pin/blade for the IC connector.