A home-theater-in-a-box system is essentially a home theater starter kit. It has multiple-channels and will turn your TV into a bonafide 5.1 or 7.2 surround sound system, but everything is generally smaller (or less powerful) to help keep the cost down. It's the perfect compromise between a high-quality soundbar and a full-fledged surround-sound system.
If you're you're in the market for a home-theater-in-a-box system, there are a couple things you want to look out for before buying. First, not every home-theater-in-a-box system comes with an AV receivers, meaning it'll you have to purchase one separate (and it'll most likely cost $300 or more). You also want to check if it supports surround sound technologies (like Dolby Atmos), which will make them sound better and prevent you from thinking about potentially upgrading your system in a few years.
Monoprice 10565 Home Theater System
The Monoprice 10565 is an excellent and affordable 5.1.2 home theater system complete with rear-channel speakers. The system does support Dolby Atmos, but it doesn't come with an AV receiver — so that'll be an extra cost and you'll want to make sure it supports Dolby Atmos as well. Bottom line, this home theater system sounds way better than its price tag and is a superb choice for small-to-medium-sized rooms.
Onkyo HT-S3910 5.1 Home Theater Package
The Onkyo HT-S3910 is our pick for the best all-around option for most people. Released in 2019, the Onkyo HT-S3910 is a 5.1 system that comes with an AV receiver that supports Dolby Atmos and will be compatible with most 4K TVs. It also has built-in Bluetooth (which most modern receivers typically do) so you can stream to the system when you're not watching TV.
Klipsch 5.1 Reference Theater Pack
The Klipsch Reference Theater Pack is a 5.1 home theater system that was originally priced at $999 when it was released in 2018, but now you can snag it for less than half that. It's a powerful system despite its size because it pulls speaker technologies (like its Tractrix Horn technology and aluminum tweeters) from the company's larger Reference line. Unfortunately, it doesn't come with an AV receiver and it doesn't support Atmos so it's not as future-proof as other options.