Marantz PM-15s2 Limited switch

Hi all, 
New to the forum, actually my first post.

My current setup is as follows : Amp- Marantz PM-8004, Speakers- Tannoy DC6 bookshelf, Subwoofer- Sunfire SDS-10.
CD- Marantz SA-8004, Tuner - Marantz ST-7001.

Im thinking of swapping out the Marantz amp PM-8004 for a Marantz PM-15s2 Limited edition.

I know specs aren't the be all and end all , but I see that although the 15 has an output of 90wpc and the 8004 70wpc, the SNR for the 15 is a lot lower at 89dB for Line in vs 106dB for the 8004.

Won't this mean the 8004 will be louder than the 15?

Thanks in advance for the comments.

No. Does not work that way at all.

Wpc is measured, while "loud" is subjective. Some amps simply sound more powerful than they measure, for example.
But even if you go by measurement, the difference in terms of decibels between 70 and 90 watts is probably only about 1 dB, ie barely noticeable.

As a general rule you can disregard power differences less than double. Even double the power the difference is only 3 dB. In other words your 70 or 90 watt amps would need to be around 150 watts to even begin thinking about power.

All of which is almost beside the point. What really matters is not how many watts but how good. Because even playing loud the vast majority of the time the output is only a few watts. Which is why Robert Harley famously said, "If the first watt isn't any good, why would you want 200 more of them?" The sensible thing then is to buy the one that sounds best, period. 

Since you already have a pretty nice amp it makes no sense to change until and unless you find one that sounds a lot better.

Take whatever you were thinking of spending and use it to upgrade your interconnects, speaker cables, or power cords. Or buy a Blue Quantum Fuse or two. 
Thanks for your input millercarbon

Didn't know interconnects, speaker cables and power cords could make such a difference.