Marantz receiver doesn’t send full band to fronts with stereo signals

After days of research and trial-and-error, this is my last hope.

I have a Marantz NR1508 with only stereo speakers, Q Acoustics 3050.

The issue is, there is basically no bass with stereo signals. If I feed it a surround signal (of any type basically, the bass is plentiful.

In speaker config, the fronts are set to ”large” and the rest to ”none”. Subwoofer is set to ”none” as well, so the crossover settings should be ignored (and are grayed out).

When I play a surround signal (a movie or a random Dolby test/demo track for example), it sounds great, and most importantly, the difference when switching the fronts between ”small” and ”large” is night and day.

However, as soon as I play a stereo signal (Spotify Connect for example, but input doesn’t matter), I get no bass, and it’s like the speakers are stuck as ”small”. Switching between small and large, there is no difference. Small also force-enables subwoofer, and setting the crossover to the lowest 40hz makes no difference. There is no difference switching between direct or pure direct either.

I’m almost suspecting some sort of firmware bug here. With a stereo signal, the speakers simply don’t get the full band. They sound completely flat. But play a surround signal and they sound rich and deep.

I’ve tried hard-resetting the receiver, tried running the audyssey setup multiple times (which correctly identifies the speakers as large) but to no avail. The Dynamic EQ of course improves the bass a tiny bit, but it’s no solution.

I’m really out of ideas here. My brother has a Marantz NR1608, which is basically the same amp, and has the exact same speakers, and the difference is huge. There is obviously something wrong here.

Since everything sounds great with a surround signal, I’ve ruled out any cable issues, bad phasing etc.

I’d truly appreciate any help with this. I really don’t know what to do.