using high end speakers wit integrated recievers

Is it possible/advisable to power (and appreciate) speakers such as the B&W 800 series line with an integrated amp, such as the Pioneer Elite VSX-21TXH?

What are the drawbacks?
Mainly the entire sonic range will be lacking and you won't appreciate what the speaker is capable of. Years ago many audiophiles used 800 matrix series with Adcom and although very good but still far from the potential they can deliver. If you are planning on upgrading and building a system then you won't be sorry.
It depends on the amp. The large Musical Fidelity ones, NuVista, TriVista, 500 and 550 would do a very good job. The Krell 300, the new one that retails for $2500, should also do a good job, it is surprisingly powerful. Gamut also makes some good ones. What you will find that the good ones are not especially cheap or small. The MF ones weight 110 lb., thankfully divided into two units. They are in another class entirely from Adcom and the like. When I was a B&W dealer I drove the 801s I demoed with a Crown SL-2 (?) , which could pulse 1600 watts. High power and especially high current capacity is necessary, you can find these in an integrated amp but you have to look carefully. There was a MF 500 for sale on here recently for $2900, I think this would be a good choice both for value and performance.
I agree with Stanwal on his suggestions, however, the OP speaks of using a Pioneer Elite home audio reciever, which IMO is bad idea. It's kind of like buying a Porsche 911 with an engine from a Ford Taurus.

Been there, done that.... there are not many shortcuts to great sound in this hobby. You get what you pay for.