I would imagine it is possible. You could copy the LPF and BPF component values from the QMX+. However, because the QMX share LPFs, and in some cases BPFs between two bands, you would likely have to give up two bands to get 6 metres. There are 3 LPFs and 4 BPFs.
If you want 40M, you could start with a mid-band QMX and use LPF 2 for 6 metres, but you would lose the 17/15 LPF. 15M has it's own BPF, but shares a toroidal inductor with the 20/17 BPF, and I would imagine there would be some interaction between the two BP filters that would have to be sorted.
It would be a fun project for a magic band aficionado...
72 de Russ, va3rr
Jason - WV3V - Las Vegas, NV.
va3rr