I gifted a 2500 to a friend and also have the 4500 mk II. The 2500 is a nice solid unit been trying to have them let me restore it finally have it back when it started dropping a channel. I will be restoring it and will swap it back for the Pioneer SX-535 I loaned them. Being inside both Onkyo units both seemed a bit overbuilt. I have a good impression of Onkyo. Take the 2500 over the SX-535, not sure when you step up to an SX-636.
Lots of good vintage units to choose from the major brands (Pioneer, Sansui, Kenwood, etc), many lesser brands (Sherwood, Nikko, Rotel, Optonica from Sharp, Phillips to name a few), and even some good store brand units like Concept (Pacific Stereo), Modular Component Systems (yes JCPenney did hifi), Realistic (Radio Shack), and Lafeyette who just put their store name on theirs and there were others. The lower power units under 40 wpc tend to sell for much more reasonable prices since the big money tends to chase top of the line units, the marquee brands and coveted series, and the more powerful units from the monster era of the late 70s when the max power ratings shot up to as high as 330 watts per channel.
You can do what I often have done. See a nice unit (even lower powered) for sale in local or regional online ads (Craigslist, Offerup, FB Marketplace, etc) look up the model here and on the web to capture other audio sites and see what comments they get. Surprising how some lower power units get talked well of repeatedly some that come to mind are the Sherwood S-7100A and 7200, Pioneer SX-636 and 737, Sansui 1000X, 2000A cheaper than the X model, 800, or even the Onkyo TX-2500 or 4500 (and the Mk II versions that followed).
Be aware a lot of these vintage units are 40-50 years old and it is surprising that some units all original are still working at that age. Often they need repair and restoration to work much less sound their best. Learn to fix them and cheap fix and repairs can be acquired and brought back to life. Ones that old usually need restoration anyway.
