It’s been a long time since I was into car audio but there’s a big gap between high end and low-end equipment. A brand that goes from middle of the road to upper-mid is probably rockford fosgate. The advantage of a company with a long history and a lot of available products is that you can usually piecemeal a system together based on identifying parts of your stock system and replacing them with choices made according to price and compatible size, all from the same manufacturer, in comparable range of quality.
If you have the money to invest in it, find an audio shop that is not a shady “$1 installation” type of racket, and at least pay for a consultation because they may have experience with van audio vs car audio. The open-air acoustics of the listening space generally dictate the quality of the sound when piecing together audio components just like any studio or music listening space. They may ask you what type of music you listen to or what your goals with the upgrade are because if you don’t want a full system change, their recommendation might go from anything like “you just want an amp and a subwoofer” to “you won’t get what you want without a new head unit”.
If you do a search for the make and model, you may find some complete systems are available for your application specifically and if you plan to do your own install or even if you just want to buy it and let someone else turn the proverbial wrench, buying something prefab (such as it were) could be the path of least resistance with at least some metric available for the results as other people will surely express their opinions on it online if they’ve paid for it.
Any custom selectively assembled car audio system made up of multiple brands and custom component choices is only going to be as good as the equipment itself and the knowledge of whoever assembled and installed it. Food is food and you can throw in whatever spices and it tastes fine unless it tastes bad, that is until you’ve tasted good food and then you understand why people who specialize in cooking food as chefs or whatever profession are professionals.
I know this is a lot to take in, but there are a lot of brands and most of them will be of comparable quality within a certain price range. Unless you’re prepared to research this extensively and have a clear goal in mind, I’d look online at shop reviews and see who is highly rated and then call and ask the cost for a consultation. In the end you might just stick with what you have, it’s a pandora’s box you may not want to open.
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