Looking for speaker suggestions

[UnklSnappy]

Here's the current setup.
I want to go 5.1 for now.
I'm have an HK AVR 3600, I'm useing the L & R preouts into a NAD 2600 amp.
The amp puts out 250 wpc at 4 ohms into a pair of Mission 780 Argonaut mark II which are 4 ohm speakers. I have no plans on replaceing these speakers currently as they are excellent sounding even though they are over 20 years old.
I'm looking for suggestions on a center and rears which will be powered by the receiver (85 wpc). Also a sub.
Should I be looking for speakers with a similar sensitivity to my current fronts.
Thanks for any suggestions.

 

[Zorba]

Check out Elemental Designs for a sub. I love mine. I have the original version of the A3-300, which is downward firing. They are also made in Iowa.

I also listened to Hsu subs, which a lot of people like, I thought they sounded fine but I went another way after learning they are built in China.