I have Tannoy Mercury 3 floor standers at 8 Ohm and just got given a pair of 4 Ohm Onkyo D-N9BX bookshelves. Plugged them both in to my Cambridge cxa60 to compare via A/B channels. Seems they sound best when I play A and B together. Am I going to knacker my amp with this set up?? If it does pose problems, are those problems only going to arise at a high volume??