Different. The 5990 is almost identical to the 1600. The 1600/2600 are sold in high end stores, while the 5990 is sold at stores like Best Buy. If you look on page 119 of the 5990's manual, you'll see it's actually 120wx7, 20-20,000Hz, .04 THD, at 8 ohms.
They get the 140 watt figure from a 1000Hz spec at .70 THD. That's a typical big box store type rating. They'd never do that in a high end audio store. They know people who shop at the big box type stores will never check the manual for these types of ratings. From the headlines, you'd think the 5990 was the best out of 1600/2600/4600 models (rated at 120/130/130 watts).