Clarity of Dialogue – Yamaha 836SE vs Pioneer SC-LX71

My aim is to make the dialogue/speech on films and dramas is as clear as possible.

I am trying to choose between the Yamaha 836SE vs Pioneer SC-LX71 (my room is relatively small so I think the LX71’s THX Select2 is more suitable than the LX81’s THX Ultra2 – that’s the relevant difference I can see between the LX71 and LX81).

I can’t find anywhere that will demo me both the Yamaha 836SE and the Pioneer SC-LX71
which means it's hard to compare against each other so I’m looking for
any feedback or advice on whether the additional £500-£600 will bring any significant increase in the clarity of dialogue/speech from my system for films and dramas.

The rest of my system is a Monitor Audio Radius R250 centre speaker with Radius R270 front speakers and Radius R180 rears (can’t change the speakers – my partner loves them), a playstation 3 for DVD and Blu-Ray, Sky HD, Pioneer PDP-428XD TV and Chord Silverplus HDMI cables.

Appreciate any help you can provide.>>

Thanks
D