"The manufacturer rates it a 200wpc/8ohms. How can it be rated higher by someone else?"
Easily, if the manufacturer really underrates the 8 ohm power specs far below what it actually measures. For example, it looks better to have an integrated amp that is rated at 200W per channel into 8 ohms and 400W per channel into 4 ohms than one that puts out 290W per channel into 8 and 400 into 4. If they lower the rating on 8 ohm to 200W (far less than it actually puts out), it makes the amp look like it doubles down into 4 ohms which is a quality highly valued by a lot of audiophiles. No one will really get upset at them either since they are underrating their 8 ohm figure. It's not like this is the first time that a manufacturer has done a rating like this. But, it can be a little misleading.
Easily, if the manufacturer really underrates the 8 ohm power specs far below what it actually measures. For example, it looks better to have an integrated amp that is rated at 200W per channel into 8 ohms and 400W per channel into 4 ohms than one that puts out 290W per channel into 8 and 400 into 4. If they lower the rating on 8 ohm to 200W (far less than it actually puts out), it makes the amp look like it doubles down into 4 ohms which is a quality highly valued by a lot of audiophiles. No one will really get upset at them either since they are underrating their 8 ohm figure. It's not like this is the first time that a manufacturer has done a rating like this. But, it can be a little misleading.