Parasound a21 upgrades


Bought a lightly used 2 year old Parasound A21 some days ago. It has exceeded my expectations for sure. Right up my alley warm mids and non aggressive highs but also dynamic and tight with lots of headroom. 
Are there any mods that are reasonable to do to these amps? Fuses etc. Can the bias be safely increased to add more class a watts? 
Also have there been any changes over the years? So is a 2 year old A21 the same as a 15 year old one? 

Thanks
mofojo
The latest version is the A21+, maybe Parasound can tell you what's different and maybe they have an upgrade program. 
Hi OP :

Luxman and Ayre are brands you should listen to which you can find in that price range used.

Best,
Erik
The JC5 is the clear upgrade at 6k, one could argue go for the A21+ and save some coin as from what I understand it's a refined A21. I switched to the JC5 after many years of musical enjoyment with my A21, I did upgrade it's main fuse twice with fantastic results , one was the HiFi tuning Silver Star and a few years later the Supreme. I do however recommend the Xlr's and a good powercable  of choice. And as noted above if your room isn't acoustically treated do so.

Thanks all,

As I said I am very happy at the moment with the stock A21 so won't be upgrading in the near future. I'm sure at some point the bug will bite! Ussually sooner than I'd like. 

I may look into the hifi tuning fuse. I am ussually very skeptical of such things but for 100 buck would not be out a whole lot and I can make my own determination. 

@jdub39 
I agree since I very much like the basic sound signature of the A21 the JC5 may be a clear path. At least from a risk standpoint. In your mind was it worth the extra cost?