Thanks for the link.omnibeard said:You could try Redhill Audio - they claim to do upgrades, so presumably do servicing too. I have no experience of using them though.
Search these forums for Pioneer A400 - I bellieve there was a thread not so long ago on something similar, plus you should find speaker recommendations.
I've used an A400 with Mission 751s (recently - a nice combo, detailed, good separation but a little lacking low down), Mission 752s (a long time ago, from what I remember a fab combo, everything the 751s offer plus more bass), and Acoustic Energy AE109s (recently, again a lovely combo). You'll probably read suggestions of using with Mission 753s too.