U use one of these here, for you can do all kinds of stuff with it, robust, very loud, and has a sub output, but to be honest I would just use the high side of your sub, should you choose one to include, for IMO I do not kie where they have it set to to have the bass kick in. So unless you have some big speakers hooked with then a sub, Id use the line, but small speakers, run them out this, to the high line of the sub, then to the speakers, and then adjust to your liking more fine tuned by adjusting the hz of the sub to be happy with what you pu8t to it to YOUR ears
ENJOY (click me)
If that is is not your jam, and looking for something little older but more more more more bad ass especially if you can find one is a old vintage JVC unit, and some Panasonics from the late 90's to midish 2000. You will pay out the butt for a working one and if you can find one with its speakers, holy crap are you in for some bad butt tunes, and the JVC units also have the USB you are looking for, but again, they are high dollar, but worth every penny, for them gigtuned speakers (yes oem called) really really kick out tight bass at max. How I know is I recently owned a "broken" one I gave to the kid down the street that helped me in the room here the line and usb input still worked fine.
You can always go look at your local goodwill for there have been times I have seen these systems show up from time to time with or without its speakers, but then speakers always I see on other days without the main unit
But little, JVC has all asked but pricy if you do not mid kick butt loud af older system, covers all you want and with matching speakers, trust me, you wont even need to hook a sub as you die from blood loss coming from your ears
Or can call it a day with the Onkyo, buy a cheap Ipod off ebay, use a 3/5mm to rca to hook ur phone or anything with a headphone jack for that matter, OR can hook up a Bluetooth adapter from amazon for it as well. It does cd/mp3/wma