No. I didn't say you could purchase the 804s for $5k. I said you can purchase speakers that sound much better than the 805s for less than $5k. In fact, you can purchase speakers that sound much better than my 804s for much less than $5k. I know. I've done it. But this isn't the thread for a speaker discussion. Just wanted to clarify my earlier comments since you asked.
Back to your original question... since I've never heard any of the other amps you've mentioned, I wouldn't venture a guess as to if the Lyngdorf would improve the sound of the 805s or not vs them. All I can offer is my experience with my B&Ws. The 2170 did sound better with my 804s vs a number of different amps I auditioned side by side prior to settling on the 2170.
Back to your original question... since I've never heard any of the other amps you've mentioned, I wouldn't venture a guess as to if the Lyngdorf would improve the sound of the 805s or not vs them. All I can offer is my experience with my B&Ws. The 2170 did sound better with my 804s vs a number of different amps I auditioned side by side prior to settling on the 2170.