For efficient speakers, how much difference does an amp really make?

Dtrandal, I concur with those that suggest that those speakers are the limiting factor. You are only going to get so much bass out of such small drivers. That said, I’ve owned a few Adcom amps, and they really do have great bass with decent detail.

They still make amps, by the way, and instead of buying a decades old used one, you might consider something from their current offering. I’ve had both the 555MS and the 555SE at 200 wpc.

I would suggest the 565SE, at 250 wpc. But, it needs around 2 volts at the input stage to achieve full power. Can your preamp put out 2 volts? By way of comparison, your Outlaw amps achieve full power with only .85 volts, or 850milivolts. So if you are getting really loud before your volume knob is at 10 o’clock, then you probably have close to 2 volts potential anyway. Depending on the volume pot scheme, that is.

Or, if your preamp has XLR outputs, you could buy a couple of Schiit Vidar amps and employ them as monoblocks(they operate as mono's when connected with XLR) for 400 watts per channel. I also have that amp btw, another great option.

The gain structure of the current model Adcom amps are all below 30 db, I believe.  The 565SE's gain is 27 db.  When I was checking out the input sensitivity of this amp, I noticed what appeared to be an error as the Adcom spec page lists it at 12.1 volts input for unity power.  I emailed Adcom and they responded within a few hours, saying the spec is actually 2.1 volts.  By way of comparison, the 555SE is 1.7 volts.

I’ve owned both the Ascend Acoustics Sierra 1 and Sierra 2 with the Raal Ribbon Tweeter. The brand is meticulously designed and tested. The components employed are anything but off the shelf, and it shows. When I put the Sierra 2 up against my Paradigm Monitor 7 V3(a tower), I was almost shocked.

Shocked at the mediocre sound I had been putting up with for about a decade. But the Monitor 7 was merely designed to be a slightly better option to the big box options back in 2003, and the industry was turned on its head since then. Still, it demonstrated to be that the Ascend Sierra 2 was a serious speaker.

Anyway, I’ve never heard the Sierra Tower, which is a different animal from David Fabrikant’s various bookshelf designs. Typically they were all easy loads, benign phase angles, and relatively inefficient. I haven’t owned my Sierras for about 3 years now, so haven’t kept up with what they’ve been up to.