Like any mix, testing your QUARK encoded mix in mono is important. Though many folks listen in headphones these days, there are a lot of mono smart speakers like the amazon echo out there to consider. Listeners through these devices will have no issue hearing your music but it is important to test your mix in mono.
You have to be especially careful because the Regular Matrix math in QUARK (the same math from the 1970s) uses -90° and +90° phase shifts to fold rear channels into the front channels. As such, when listening in mono, rear-panned audio has some phase cancellation. Most drastically if you pan a track 100% to the center-back, the audio is completely cancelled.
Modern mixing techniques regularly have to address some of this compromise, especially when utilizing mid-side processing to “widen” a mix. Ultimately, use your ears.