it sounds great but looks funny?
Here's a news flash... the styling has not changed drastically since the time your amp was made, particularly where integrated amps are concerned. Even moreso with NAD. They are still utt bugly but sound great..
To take advantage of surround sound...
...you'll need, along with a multi-channel amplifier/receiver, at least three additional speakers to go with your existing two speakers. Also, a subwoofer is not mandatory but very, very highly recommended in order to avail yourself of the dynamic visceral effects that sells HT to the masses.
As for an integrated amp vs. a receiver, well, a receiver is simply an integrated amp (simply a preamp/power amp on one chassis) with a tuner thrown in the mix.
As to what's available in your price range, I may not be much help. I'm in the US and from the pound sterling sign you use, I assume you are in one of the British countries. There's a whole lot we have access to that you don't, and vise versa.
From what I gather from reading What HiFi? years ago youse guys seem to have more of an interest in mid level "stereo" than most people (and marketers) here in the states. If you choose to stay in hte two channel world, I believe this can work towards your advantage.
So, which way do you want to go? Multi-channel or simply replace the amp/receiver with a two channel unit?