As I currently own and use a B&W HTM61 as my center channel, I will have to disagree. It is quite excellent for a center. Reproduces dialogue very clearly and is easily driven to loud levels. However, I do agree that you should not mix and match the LCR, as that is arguably the most important part of the system besides the sub. However, you CAN get a different sub than your LCR (or speakercrafts, or whatever.) What would help narrow down Sub suggestions (as others have already suggested, you will get the typical "everything" answer) is a specific price you want for a sub and your expectations.
If one is going to make a simplistic assessment of the value of different alignments, it would be that sealed/IB goes the lowest, at the highest cost per dB; horns have the lowest cost per dB at the expense of size, and vented box characteristics lie in between the other two. None is inherently superior across the board, neither is any inherently inferior across the board. The one to use is the one that fits your response and output needs, available space and bank account. -BFM