Both amps you have mentioned are rated at 200 watts rms at 8 ohms . This would be more than enough to run your speakers I would think .
Using either the M200 or 770 would give a sonic improvement to your system .

How do you have your speaker wire terminated ? This could be the source of your Dennon problems . The 2805 should be capable of driving your speakers as well . Granted the Dennon would not do as well as the M200 or 770 amps but it should not shut down when played above moderate volume . Are you sure you don't have a wire touching the housing of the 2805 . This would throw the rec. into protect mode if even a single strand of the twisted wire were in contact with the rear panel . You may want too check the speaker connections as well .