I have two of these simple Sure kits from Parts Express to try as part of a biamp scheme for my speakers. PE has a chassis for the kits available but on back order at this point, so just using the boards.
At $44 for the board, $10 for the volume control and $20 for the chassis they are very affordable. I am going to try it with 24VDC from batteries and see what happens.
Looking for feedback from folks that have tried them in applications on the good and bad. So far in trials with some test speakers and a switching power supply the first board sounds very good. This is using the volume control add on with the PA board.