I don't think there is another tier. There is a limit to how much performance you can squeeze out of complete 2.1 systems. Higher tier based on price maybe, like the discontinued Jamo i300, and perhaps Focal Little Bird? But I wonder if they have enough performance difference to justify the price difference.
This is how Promedia can last for so long and people are asking how to repair their 10-year-old units. Because there is nothing to upgrade to and nobody has bothered to make one.
Because to get better performance than 3-inchers, you need to go 5-inch, or 6-inch, and by that time, people realize why would you need a 6.5-inch sub when your satellite woofers are also 6.5-inch? So they realize they can actually sell the speakers without the sub. Bigger subs are still needed for lower bass, but at this point they become optional instead of a necessity.
So it's not that higher end 2.1 systems can't exist, but due to logical choices, they don't. But they can.
Edifier S301, but they call it 2.0+1 instead of 2.1 because it can operate in 2.0 mode too.
