It has been a good few years since Harmon Kardon had a 'wow' moment in the audio world. Its efforts have been concentrated in the AV arena for far too long now, but, it seems, high-quality audio has never been out of the firm's mind.

The new HD 990 player and HK 990 amp are products with a difference. Actually the CD player isn't quite so unusual, though it does have a few less common features that we'll come to in a minute. The amplifier, though, turns out to be a thoroughly different colour horse. Yes, you put a little signal in one hole and it comes out of another much bigger, but what goes on between the two is – or can be if one chooses – a lot more complex than pure amplification.

Harman Kardon has a well-established presence in home AV, where things are done a bit differently. In such circles, it's quite normal to have a lot more stuff going on in an amp than mere amplification. Features like video source switching are never going to be much use on a two-channel audio amplifier like this, but digital inputs and digital signal processing can do a lot of useful things, including room response measurement and correction and this is where the HK 990 comes into its own.

HK has been rather clever with all this. Realising that not all users will want all this processing in the signal path all the time, the HK 990 has been provided with sophisticated routing options for each input, so that some or all of them can be directed through an allanalogue path from start to finish. Since basic switching functions are carried out by relays, as in many current amps, this means that the signal path is not necessarily more complicated than in much more basic amplifiers.

If you choose, though, you can send each input (or just some of them) via a digital chain that first samples analogue inputs at 96kHz and then applies room correction and/or digital tone controls, before converting back to analogue and amplifying to loudspeaker levels. Basic analogue functions are kept simple, with little more in the path than relays and minimal buffering, while digital stuff is handled by high-power DSP chips on a dedicated circuit board.

The enormous size of the amplifier is dictated by a combination of its high power rating (150 watts into 8 ohms, though we had no trouble extracting 200 watts from it in our tests), a high standing current which causes the first few watts of output to be delivered in class A (and causes power consumption to be a high 180 watts at idle), dual mono operation of the power amplification channels right down to separate mains transformers and the simple need for a lot of space at the back to accommodate analogue and digital input and output sockets.

The front panel design is quite crafty in that it looks a bit like a preamp resting on top of a power amp, but at the end of the day this is a very big chassis. Another area where HK shows its involvement with AV is in the provision of subwoofer outputs. One or two subwoofers can be catered for and the automatic room/speaker correction process, the rather cringe makingly named 'ezSet/eQ', includes them in its setup process, which should aid subwoofer integration considerably.