As others have said you can't get around physics. I've been there and done that with similar
computer speakers (IMO the best in their day) I found the ping-pong effect of the sound source moving from speakers to sub and back to be disturbing even with a computer. My advice is to listen to the advice of those that recommended 4-6" in-wall on on-wall or bookshelf speakers. They will pair much better with a sub. Unfortunately, I don't have a recommendation in your price range because I have not auditioned much that size in a long time. It's your money and if you must have tiny then that's up to you.
As for used receivers, I wish you luck. I tend to hang on to receivers until they die and the only used receivers that I've ever bought had things wrong with them. Refurbished might be a better choice but I'd concentrate on speakers first because you choose your receiver based on the speaker's requirements.