Sending less than RMS recommandation

Hello guys,
I'm designing a very, very low sub using WinISD.
Using 2 Acoustic Elegance IB15HT-8 in isobaric application and a 4th order bandpass, the bandpass is like 9.9 Hz to 28 Hz (-3dB).

Problem is : cone excursion is easely too high (I couldn't find better speakers for this application, if you have an idea, tell me!).

The cone excursion is ok for a signal of 90 Watts (so 45 watts per loudspeaker since there are 2 in derivation).
But the RMS recommandation for one speaker is 300 Watts RMS (600 Watts MAX).

Is it ok to underpower it that much ? What happens, beside a lower SPL ?
Distorsion ? Noise level too high ? Can't find this specific information.

I mean, a sound level of 98 SPL is ok for me, because it's for a home application.
So if there's no downside except volume, I'm fine with it.

Is there other downsides ?
Thanks !

ssbb1fire wrote: Is it ok to underpower it that much ?

Yes perfectly fine.

Thank you very much guys for answering precisely my questions !

Yo each his own of course, but what sound do you need or want amplified, because next to no music has any info in that region. And if it is for amplifying something like a pipe organ, what gear will let those frequecies through in the whole chain of microphone-mixer-amplifier...

It's more of a crazy projet to shake my house.
It's use will be for movies and very low bass in some synthwave music (an to allow me to use this part of the specter in my music).
And to be honest, I just wanna brag that I went lower than the genelec 7380 AP that will cost twice the price.

Thank you so much, this information is so interesting and helpful !

I have to introduce myself a bit here.
My name's Samuel, I'm a 3rd year student in acoustics at Le Mans, in France.
For almost 3 years, I've done manipulations in classes in order to measure several things, such as frequency response, directivity for example. But we've always been taken are of, such as we didn't have any troubles other than the measure itself.

It's the first time I have a situation where the driver isn't the source of the problem, and have no clue how to test my measuring the equipement within the chain.
In two months, I've designed several enclosures and simulated some loudspeakers systems, but never made any electronics besides passive crossover filters.

Do you have any advice on how to choose the processor/amplifier for this kind of application ? What to check ?
Also, me wanting to create my own amplifiers (or active filters), do you have any references, books or youtube channel I could check ?
If I make everything myself, It's way easier to control everything within the chain.
Do you also have references for measuring the signal chain too ?
To check its compatibility with this project.

Thanks a lot man, you've made me think of problems I wouldn't have tought of myself before I ran into them.