I am with you on the pricing, for the money the 4400 would the better value and more powerful. I think the link price changed for the 6012 since the last time I used the it. Blame google.
In the UK it's 5 years for either the Denon or Marantz, although I think as was mentioned previously it's not internationally transferable.
Can't say I've particularly noticed a "warm sound", maybe its my settings.
You got me curious about the pricing in the UK so I went and browsed the websites of a couple discount hifi/ht stores. From what I can see, the pricing for comparable D&M models are quite different in terms of both list price and discounted price, and cannot be compared directly. It does appear that in the US, the X4400H has the best deal, though that $799 discount price has not been seen recently. In the UK, the SR7012 is the one to beat. The X6400H price is still holding well, but as soon as the X6500H is out, it has the potential to drop like a ton of rock, not so much in the UK, but in NA.
USA
X4400H - $1599/Dis:
$799.......................................... SR6012 - $1499/Dis: $899
X6400H - $2199 ..............................................................SR7012 - $2199
X8500H - $3999 ..............................................................SR8012 - $2,999
UK
X4400H - £1299/Dis: £799 .............................................SR6012 - £1099/Dis: £749
X6400H - £2299/Dis: £1599 ...........................................SR7012 - £1699/Dis:
£999.9
X8500H - £3499................................................................SR8012 - £2,699