"Reference" is having the ability to 105db. Few people listen quite that loud but it's a solid number to be able to achieve.oops rechecked made a mistake of putting 9 meters instead of 3 meters lol. The result is now 98.2 db
When i change the Amplifier watt to 80 i get a result of 99.5 db. Thats if i go for the Nad C268
When i change the Amplifier watt to 150 i get a result of 102.2 db. Thats if i go for the NAD C275BEE
That said, if you are on the fence about it, try it without. Raise the crossover, to let the sub do more work, to see what having more power is like. THEN try it with an amp and see if that makes you happier. If not, return or sell the amp.
In other words, you clearly do NOT need an amp to get started. You will get good loud sound without one. But there is a possibility that an amp will improve things. So the experiment is worthwhile, especially if the 'raising the crossover' experiment is pleasing, on its own.