wireless connection to portable speakers or phones

i want to listen to music from my audio system, up to 50 metres away from it (e.g. in the garden) either via headphones or portable battery-powered speakers. is it possible to buy a device which will plug into a pre-amp and transmit the sound; together with something compatible to receive and play it in a way that might outperform an ipod based approach?
These guys are the best as I see it. Three models; 1 w/line out (no amp) and 2 w/speaker out (amplified)