No sound difference IMO. You can buy Denon PMA 720AE for as low as 170GBP, where as you'll get Marantz PM6005 for 350GBP. and PM6004 is no longer available in the market. PM 6005 has an in-built DAC. Whereas PMA 720AE has pre-out, which is useful for future expansion or if you want to add a sub. At present scenario, Denon PMA 720AE is the best choice in terms of sound, price, aesthetics and for future expansion.