Johnny, beware of demonstrations by salesmen. There's no reason why the SC-35 would sound better than the 6005 in a fair comparison at equal volume levels. So no, you won't get better sound with a more expensive receiver.

To stay under the budget you mention, I'll recommend that you get the excellent Onkyo 709 for about $550 which I linked in my previous reply.

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Enjoy the music, not the equipment.