What Power Amplifier Should I Buy?

Both Stereophile and ASR test show plenty of bass down to 30hz. Your 14x19x8h room looks fine, but the other impedance show the F208 is harder than average to drive. Conclusion is that you don’t have enough power. Also, if one defines “average” needed power to run most speakers, seems to be in the 150-300watt at 8ohms range, somewhat doubling down to 4ohms.

If you love your amp, I suppose you could try to fill in the missing bass, but my preference would be to get the bass from the speaker since it’s matched to the other transducers (mid treble).

Maybe you can test by borrowing a more powerful 4ohm amp?

Two subs increases bass headroom by 6 dB, as well as significantly reduces peaks and nulls from room modes. You can’t EQ out a null, which can be 15 dB or more deep, and worse, the nulls are in different parts of the room, so even measuring them is tricky. Two (or more!) subs fill in for each other, since they are separated from each by many feet (preferably as far apart as possible).

A 6 dB increase in headroom is nothing to be sneezed at. 3 dB comes from having twice the power (two plate amps instead of one) and the in-phase in-room summing doubles speaker efficiency, so the net gain in headroom is 3+3 dB, a fourfold power gain. That’s equivalent to either getting 6 dB more efficient speakers (think horns) or 4X the power amp, assuming perfect loudspeakers with no power compression.

In reality, speakers with efficiencies in the 87 to 90 dB/meter range typically experience power compression with amplifiers more powerful than 100 watts, so a 500-watt Class D power amp is not necessarily the answer ... any loudspeaker will sound audibly "squashed" or distorted if too much goes in. Remember, a 92 dB/meter/watt speaker is only 1% efficient, with the other 99% of those expensive audiophile watts doing nothing more than heating the voice coils.

It's a shame you don't have measurements.  Also, putting an EQ just in the path of your sub is a very good idea. 

You may be suffering peaks that need to be clipped that would let you raise the sub level. 

For an amp with Oomph I like Luxmans, which have amazing bass extension but this may not help you much with a sub and high pass filters.

@erik_squires 

Moving the EQ to the sub path is a good idea. I do however, make adjustments to frequencies higher than the 120 Hz I now use as XO.

What kind of measurements are you referring to?

@lynn_olson 

I agree that another sub would help.

I'm confused by your statement about power requirements. Did you mean to say that any amp over 100 W will push the drivers into compression (does this mean non-linear?).  Therefore any amp over 100 W is not recommended for speakers that have the sensitivity that the Revel f208 does.