Media Markt near Leroy Merlin in Tarragona have a wide selection of cordless headphones (Senn/Sony/Philips etc). I haven't looked, but I would imagine they have speakers too.

When you say hifi, do you mean hifi? You're unlikely to get anything hifi that's smaller than a postbox and very unlikely to get cordless hifi - most buffs prefer heavier wire to no wire.