Scott,
If HT(over music) is your main function for this system,
I would go the outboard multichannel amp route with your 6005 as pre/pro as first option. If then you feel your system is lacking and want better 2-channel performance, then replace receiver with a quality pre/pro or just add a stereo preamp with an HT bypass feature.
I think this B&K amp(or similar model) will mate very well with your B&W's and have no trouble driving them.
http://app.audiogon.com/listings/multi-ch-b-k-components-reference-7270-mkii-7x200-watts-per-channel-power-amplifier-2012-09-09-amplifiers-45385
Or even this Parasound or similar model.
http://app.audiogon.com/listings/multi-ch-parasound-5125-newclassic-five-channel-amp-2012-09-28-amplifiers-84103-salt-lake-city-ut
Bill