I have generally been a fan of Adcom as a maker of good, entry-level audiophile gear. I still think that many of their products offer excellent value -- particularly the GFP-750. Artemus is correct in his advice to avoid the 5800. The 5802 has gotten good reviews, and was highly rated by Stereophile. I have a couple of cautionary notes, however. First, if you have not actually seen the 5802, be forewarned that it is quite large. Second, because it runs mainly in "Class A" mode, it runs hot, so it will need lots of ventilation.
I have owned quite a bit of Adcom gear in the years since 1986. During most of those years, Adcom had its products manufactured in Taiwan, where there were a number of state-of-the-art electronics assembly facilities. Several years ago, however, Adcom moved its manufacturing to mainland China, and I believe they had some moderately bad problems with quality control.
If you are willing to spend $1800 for a good power amp, my best recommendation is to buy either a Bryston 4B-ST, or a Marsh A400. The Bryston has a bit more power than the Adcom 5802, is more compact, generates a lot less heat, and has a transferrable 20-year warranty. I bought my Bryston 4B-ST from a dealer for about $1700, and I'd be happy to provide you his E-mail and phone number if you drop me a private note.