5 channel upgrade vs 2 channel upgrade

First time poster here. I am planning to buy a new amp in the next few weeks and did have my mind set on the Parasound A51. But then I saw the new A21+ Which appears to be a significant upgrade to this line, and read a very enthusiastic review. In general time with the system is split between Video and Audio so I’m struggling with whether it’s better to upgrade all 5 channels or really upgrade 2. My system consists of an Anthem MRX 520 Receiver, Blusound Node2 streamer, Rega P6 tt with Ania cartridge, Rega Aria phonostage, and Audio Monitor Gold speakers (200 fronts, 350 center, and FX rears).  I recently added a PS Audio P15 power plant. I did talk with folks from Parasound and was told there is no current plan to upgrade the A51. Any advice and/or opinions are appreciated. 
A 5 channel amp can't match what a 2 channel amp can do in stereo mode.. If I were you, I'd upgrade the 2 channel amp now and save for their 3 channel later down the road.. In the end you'll have the best in both movies and music..
Really nice choice of speakers.

Given what you already have, I’d stick to the A21+. The main reason is you probably already have more than enough power for the remaining 3 channels, but you lack a sub.

Better to increase the power to the L and R, and run them full range, while running the other 3 as "small" speakers. Divert the LFE channel to the L and R.


If you want more output than that, you don't want a bigger amp, you want a sub. :)
Why not Anthem’s MCA225, or 525 over the Parasound, or go to Anthem’s P2?
Appreciate all the feedback. Just after I posted I realized I’d forgotten to mention the JL Audio E112 sub in my system.  I am wondering how that would affect Eric’s response?
Cbrents - I’ll look at the Anthems. Have to admit I’ve lusted after Parasound gear since I was a teenager and they were way out of my price range. 
If you already have a sub, then I don't think you'll have any issues. 

I'm not sure if the receiver lets you turn off unused amplifier channels, but I also think that adding a really nice 2 channel is plenty good.

Personally, I have a Luxman integrated and planning on adding an Anthem for the remaining 3 channels + HDMI switching.