Fosi Audio Bluetooth Subwoofer Amplifier 2.1, BT30D Pro Subwoofer Amp with TPA3255 Chips 165W x2+350W & Bass Treble Control, 2.1 Channel Sub Amplifier for Desktop/Outdoor/Bookshelf Speakers

WiiM Amp Ultra. Streamer + Amp + Bluetooth + sub out. No apple airplay, though. And it’s on sale today on Amazon due to Prime Day. $450 instead of $530. A wee bit out of your price range. https://a.co/d/07XEEamM You didn’t mention streaming capabilities. If you only care about Bluetooth and sub out, then try Fosi Audio - https://a.co/d/03zGFkcp $100 after coupon enjoy!

I bought a 2.1 channel amplifier so I can power my 2 normal speakers and then it has a built in sub frequency and sub volume so I can fine tune the subwoofer to however much bass I want. https://a.co/d/0dxsMzkL It has worked great!