I was not aware of that limitation for either said Edcors or the Akai M8 output transformers. May I prevail on you to suggest an alternative?
If your plan is to only ever build one amp and you want it to "do it all" buying larger and more expensive transformers might be the best option.
But I've learned that you can't really assume that something larger and more expensive will necessarily sound better. And there are alternative strategies which allow you to have plenty of low bass without spending so much on OTs. This is especially handy if you expect to be building more amps in the future.
In general, the main difference between smaller, less expensive, OTs and larger, more expensive, ones is their ability to reproduce bass frequencies. The rolloff points will vary but the biggest difference is probably under 50Hz or so.
You might want to consider just how important this is
to you. Everyone has different needs. YMMV, as always.
Some music has a lot of content under 50Hz and some has relatively little. Many speakers can't really reproduce much, if anything, below that either. And, of course, everyone's hearing is different too. These are all important factors. An online tone generator can be helpful in evaluating your needs.
I had my most recent build breadboarded for quite a while using a pair of little SE OTs pulled from an old console amp. I ordered a pair of Edcor 15w GSXEs for the build, which took about 3 months to arrive. The Edcors weigh in at 2lbs 9.5oz while the little console OTs are only 14.5oz. So I figured the bass would be better and they would be a step up.
This was the first time that I've purchased new, modern production, OTs for a stereo build. I've always used junkbox OTs scrounged from various sources. I decided to give the Edcors some break-in time - around 36 hours - without listening to them before giving them a serious listen.
The Edcors were really nice and, as expected, they did go lower in the bass.
But, for this amp, I actually preferred the little console OTs, which is
not what I expected. They seem more extended on top and the mids are more detailed and liquid. They reproduce the subtle textures of strings and horns better.
A lot of the difference is in the soundstage. It seemed to be a bit wider with the little console OTs but they're especially better in terms of depth. The difference in detail is most evident in the way instruments seem to inhabit their own space. The effects of reverb on more modern recordings, or natural room sound on more traditional jazz, is much more evident. The Edcors reproduce a bit of that, but not nearly as much, and their soundstage is not 3D like the console pulls.
Don't get me wrong, the Edcors were impressive, and I plan on using them on another project. But when I A-B'd them I noticed the difference. The little console OTs produce more foot tapping and head bobbing, they just swing more.
Since I do occasionally listen to music that has more low bass, I picked up an inexpensive combination of an active crossover and a Class D amp. The total cost (~$180 shipped) was less than the cost of a single large, high quality, OT. Adding a sub is another option, of course.
I find the versatility of this approach very appealing. Since I know I'll be building more amps, I'll end up spending much less on each of them since my "bass system" can be used, whenever necessary, with any of them.
And, since it's harder for an amp and the main speakers to reproduce bass frequencies, there are additional advantages to shifting that burden to a system that's optimized for bass.
Such an approach may not appeal to everyone, of course, but it's something to consider if it meets your needs.
