There will certainly be an improvement, but an optimum will sound different. Then it's better to do without new additional subs and replace the existing subs with ones that play precisely. But even a booming, imprecise reproduction can be pleasing.
ART expects a system that plays as precisely as possible. The swing-out behaviour of the SVSs is counterproductive, regardless of whether the sub outputs a correction signal or the regular channel signal.
The Oppo manual describes why this does not work. You can only send DSD to PCM converted signals to the M33 via the HDMI output.
Have you installed an HDM-2 or are you using the HDMI ARC on the TV?
What is the problem with the remote?
T+A A200 (purifi) with switchable DF:
'A high damping factor tends to produce a more clearly defined, very precise and analytical sound image, whereas a reduced damping factor produces a more warm and softer sound image.' <- extract from the manual