QMX(+) can technically tune anywhere, you can go into the configuration and adjust the band RF ranges so you have full control over what frequencies the QMX(+) will attempt to tune. These configurations are there so a law abiding ham can keep themselves from making the silly (and illegal) mistake of transmitting out of band.
But it has band pass filters around the ham bands, so you’ll lose sensitivity the further you get from a ham band in general. There would be some places where you wouldn’t lose sensitivity- the 10m and 12m band use the same filter, so you would get full sensitivity between 25-28 MHz. As far as I’m aware you must select a band pass filter and cannot bypass without a hardware mod (I honestly wouldn’t be surprised if Hans put in a bypass for diagnostic purposes but I don’t know). There is almost certainly a way for you to make one of the band pass filters very wide, but this would be a substantial modification, requiring you to figure out the inductance values yourself.
On the Tx side the issue is low pass filters. You can configure which filter bank gets used, so you could configure it to transmit on any frequency. But the filters are designed specifically to keep the the transmissions clean and legal- there are certainly frequencies where you would have to select a low pass filter that does not suppress a harmonic to legal levels.
Footnote: the 160m band has issues on the QMX+ but I’m pretty sure that will get fixed in another firmware release. But for now the useable range is ~3.5-54 MHz and not all the way down to 1.5 MHz.
