Sure, with efficient speakers (like yours), not many watts can be an awful lot of fun, but let's face it, most people are running 85-87dB SPL@1M/W speakers these days. They need more, undistorted power than the little Allo can do, unless you take the TPA right up to the V+ limit of around 30V.
18wpc is completely inadequate for high fidelity reproduction. A capacitance multiplier does not provide additional power either. It provides power supply/noise/ripple rejection.
But why is 18wpc not enough, especially if it is used as a desktop amp at roughly 1m?
I know my listening levels (and most peoples) are not normally over 90db for extended periods of time. My office levels are usually much lower than that.
So if you have 85db sensitive speakers and are within that 1m for desktop use, you should have extra power on hand.
1w for 85db/87db
2w of 88db/90db
4w for 91db/93db
8w for 94db/96db
16w for 97db/99db
32w for 100db/102db (requires better power supply)
I’m pretty confident that most will be more than satisfied with 97db/99db extended listening capabilities if they have 85db/87db sensitive speakers. This isn’t bass reproduction, 97/99db mid to high frequency reproduction is loud!
This also can be increased (as shown above) by getting a better power supply and/or more sensitive speakers and/or lower impedance speakers.
I don’t think I’d use it for HT, but I’m definitely thinking about picking it up for my office where the speakers are well within 1m. Sure the case isn’t my favorite, but I could just hide the amp if I really wanted to.
Edit* I just tested my listening level using REW and my calibrated microphone (also verified with decibel x iphone app) and I was about 70db with it peaking at 75db for louder listening, and 65db-70db for more comfortable office listening. This was with subwoofer turned off.
So that means I would need ~ 0.125w on 85db sensitive speakers to listen at loud listening for me.
0.5w for 82db
0.25w for 79db
0.125w for 76db