Best answer by Kumar
Opposite of the speakers is NOT a Sonos recommendation as such: all they say is keep the Sub wherever you want to. But best results for music from a 1 pair, I have found, is when the Sub is kept somewhere between the two 1 units, in the same plane. Exact centre is an ideal that isn't needed, but close to centre is always good. If that is done, and the 1 units are kept with the same care used for "HiFi" speakers, Trueplay will often not change the sound signature because no change is needed; and the sound quality is as good as most traditional set ups at up to twice the price point.
Finally, if you like the sound of your old speakers, that is more of it being a subjective preference for their sound signature and not a dynamic range lack in Sonos. Why don't you use the Connect Amp with these if the preference is strong? You should get the same exact sound if you have not relocated the speakers, and if you keep the other Sonos units turned off. And if you deploy the Sub as suggested with the Connect Amp, you ought to get the preferred sound made better via the Sub, if the old speakers are not as bass capable as the Sub.