I can't say for sure, but I think you're going to start to struggle with performance and I wouldn't want to spend a lot of effort on it.
It is already a challenging to get good 6m performance from the QMX+. You would have to redesign the filters for 4/5m and you might still get poor performance due to being close to the limit of the si5351 chip (the frequency source), as well as the fact that parasitic capacitance on the PCB is going to start to matter. You might also have to modify the firmware, so it might end up being a lot of effort for the modification.
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I can't say for sure, but I think you're going to start to struggle with performance and I wouldn't want to spend a lot of effort on it.
It is already a challenging to get good 6m performance from the QMX+. You would have to redesign the filters for 4/5m and you might still get poor performance due to being close to the limit of the si5351 chip (the frequency source), as well as the fact that parasitic capacitance on the PCB is going to start to matter. You might also have to modify the firmware, so it might end up being a lot of effort for the modification.