I have had my 606s for over 18 months they are placed either side of a 320mm fireplace/chimney breast and 220mm from the back wall without any toe in and they sound excellent with a superb soundstage.
They replaced a pair of Spendor D7s the 606s are the same height and depth but slightly wider than the Spendors.
When the dealer brought the demo pair and set them up he initially placed in the same position as the D7s but was rather surprised that he had to move them closer to the rear wall to obtain the best results.
The improvement in the sound stage after moving them closer to the rear wall was rather surprising to say the least.
I had the 88s and now have the current Titans. They were both set up with the help of my local Naim dealer and positioned and adjusted after protracted listening tests.
Both pairs sit in the identical spike marks on the carpet and the mid point of each speaker is about 70 cm from the rear wall. The speakers are very slightly angled inwards to the listening position.
Both are at least 60cm from the nearest corner.
Their sound-stage is outstanding: particularly relevant for me as to a listener to predominantly classical/symphonic and opera music, but also jazz, R &B etc.