At times AV and even multi-channel audio can be difficult to understand and to keep pace with. The first well-known surround sound system was Dolby Pro-Logic, which was the first opportunity to have movie like surround sound at home. Today the universal standard is the 5.1 set-up: this uses five discrete audio channels plus a low frequency only extra channel. However, as always, technology is constantly evolving and refining so that what was state-of-the-art five years ago is verging towards being obsolete. In designing the Compact System, Castle were very much aware of these problems and were determined to find engineering solutions that allowed the system to be developed alongside the technology. This has been achieved in two ways: by the careful optimisation of the drive units in all the Satellite, Centre L.C.R. and Dipole so that they all integrate fully with each other; and by the use of quality components in the crossovers. This has resulted in a series of speaker systems that can be mixed and matched to suit any AV or multi-channel music option. This means that you can start with the basic 5.1 package and upgrade to 6.1 or even 7.1 later. Such is the flexibility of the Compact System that even if in the next few years the movie standard changes to 8.1 or even 9.2 then the Compact System should be able to accommodate these developments.