With any satellite system, improving the sub improves the sound from the satellites - you'll find a fuller more natural sound, and also a sweeter treble. So if you want as discreet as you can, try the T series out with a few other subs. The T2 sub doesn't get the best from them. We're looking forward to getting the R400b sub in which should improve the system greatly. Using force cancelling drivers, this is likely to be the most accurate option, so may come across as a little bass light to some. If so, the B&W ASWCM10 or the Monitor Audio RXW12 will be worth trying.
It will also be worth trying out the B&W MT60D package. The sub for this package is basically the same arrangement as the KEF R400b sub, but also has built in DSP just like its big brother, the DB1. This has presets too, so you can store more than one setting. The new M1 satellites are excellent. Given their size, they seemed to be giving the Apex a run for their money - we'll see once they've settled down a little more. They produce a big, 'out of the box' sound, and are very clearly defined. Anyone looking around the £2k mark should have these on their shortlist.
And of course, if you can stretch to the Apex package, and their size isn't an issue (depending how discreet you need to be), are definitely worth trying.