I currently have an old ALTEC LANSING VS3251 70 Watts 5.1 and was looking at the Logitech - Z506 to replace it. 
I have some Best Buy rewards money to spend, that is why I am choosing the Logitech specifically.
The specs seem about the same. Does the technology advice to sound better even if the specs are similar?
Looking for some input thank you.
 
OLD SYSTEM: http://www.newegg.com/Product/Product.aspx?Item=N82E16836113007
 
NEW SYSTEM:  http://www.bestbuy.com/site/logitech-z506-5-1-surround-sound-speakers-6-piece-black/1215025.p?id=1218236333141&skuId=1215025&st=pc%20speakers&cp=1&lp=13
 

I had those Z506's for a short while cause I thought my Altec Lansing's went out on me, but it was just a bad audio cable. Those Z506's are pretty decent for the price, but the rear speakers are pretty weak.
 
Personally, I want one of those Z906 speaker sets... I've almost bought them a few times when Logitech sent me a 40% off deal a while back. But I all ready have a Onkyo receiver and two really nice BOSE stand up speakers that are not being used, so those are going to be my replacement. I also have a 12" subwoofer that I currently have no use for, so I will be hooking that up for fun as well.

Im using my old klipsch promedia 5.1 speakers, with a pioneer sub and a receiver i bought at best buy. It actually replaced those z506's and it sounds at least 100 times better. Don't buy those 506s, they are literally garbage and they break and sound bad in days. Honestly, even though my klipsch pro media 5.1 amp went long ago, the speakers are still some of the best you can get for PC audio, and they can easily be powered by a receiver.