I use now 40w 2.1 system which makes thumping noises when idle, so i want to replace it, my brother have logitech z623 i heard how thoose speakers sound, but i found on amazon that z906 is 200 pounds and z623 is 130, and i cant decide, i mainly using with desktop as 2.1 system because there is no where to put rear speakers and center speaker but, that price dont let me decide buy more powerfull speakers for 70 pounds more or stick with smaller system which i heard how it sounds?