Further thoughts :
If on pwm , then there are 8 wires to the receiver port , two being power to the rx , 6 others being one-signal-per-channel
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Suggesting you are maxed out at 4 for quad control , 1 for fm , 1 for alarm.
More channels available , I believe on ppm.
Lemon rx , 8 channel ppm with satellite has worked well for me.
Or satellite on its own.