Speakers, HDD music and different rooms

Hello, I am loomking for some suggestions please.

I am moving soon and the new property will require a new set up for my PC and speakers. My main problem is that the PC (and 7.1 surround sound speakers) will be in the study (upstairs), whilst we will want to listen to music contained on the INTERNAL HDD whilst downstairs in the lounge. We don’t want to upset the neighbours, so simply turning the speakers up is not an option. We want to entertain guests in the lounge and not necessarily the study. I know there are several options available but each at a different cost, quality and pros/cons.

The other thing is that it would be nice if we could benefit from using whatever solution is most practical (in terms of speakers) for the TV in the lounge.

I know of the:

* Logitech Wireless DJ Music System (but would need to buy a hifi)
* Logitech Z-5450 Digital 5.1 Speaker System 315 W RMS THX Dolby Digital & DTS (have no idea how I would set this up to work in a room on a different level of the house)

Any suggestions?

Here is the very latest and my inventory thus far:

[li][B]Squeezebox Duet[/B] [U]£214.00[/U] [I]For streaming music from my PC to the amplifier[/I]
[/li][li][B]Yamaha AX863SE[/B] [U]£550[/U] [I]including 5m of QED micro cable with airlock plugs, a 5m sub cable and an HDMI cable, Black Mission Floorstanders and a NAD Tuner[/I]
[/li][li][B]Tannoy SFX 5.1 Speaker System[/B] [U]£146.76[/U] [I]Perfect companions to the Yamaha AX863SE[/I]
[/li][li][B]2 x Tannoy SFX 5.1 Speaker Stands Black Pair[/B] [U]£87.98[/U] [I]Specifically designed for the speakers purchased[/I]
[/li][li][B]Panasonic DMP-BD35EB-K Profile 2 Blu-ray Disc Player with BD Live[/B] [U]£177.14[/U] [I]Plays Blueray discs and upscales CD and DVD to 1080p[/I]
[/li][li][B]2 x 1.8M HDMI to HDMI Cable[/B] [U]£7.92[/U] [I]Gold Connectors - For Use With HD TV’s / Xbox 360 / PS3 etc [/I]

A grand total of £1183.80

Still need:

[li]Wireless router
[/li][li]AUX cable for the Squeezebox to connect to the amplifier