I have a Phoenix card installed in an Aristo Mikado. It has really good quality sounds, but they are processed--you can hear reverb on them, for example. They have been "sweetened" in various ways by Phoenix. Most people like the sound of reverb--I do, most of the time--but on my train I find it annoying and distracting. I hear a reverberation on top of the whistle and chuff that isn't accurate to the landscape the train is moving through. But most people will hear the sound of the Phoenix and say "hey that sounds good" because of the reverb. It's the same reason they put lots of reverb on a mediocre vocalist
My Phoenix card failed after 4 months of use. I sent it back and they fixed it right away--came back last week after a very fast turnaround. In my opinion unless you're using DCC it has more features than you can use--using aristo's train engineer onboard and track power, I can't trigger a lot of what it can do. I should add that I don't have the programming cable either. That adds a lot
I would look at QSI--were I starting from scratch today, I'd get an airwire throttle and QSI cards--good quality sound, but sound and remote control are integrated so you can control the sounds more easily.
Also in my opinion--which is based on years as a semi-professional musician, mostly as a bass player--the size of the magnet has really nothing to do with the quality of the sound. We're not taking about 200 watts here, we're talking about two watts. Magnet size generally varies with power handling capacity, and with the material the magnet is made of. A bigger magnet doesn't make a speaker "sound better", it mostly just changes the power handling capacity. The single biggest issue effecting the sound for G scale, far and way, is the enclosure. What's missing in G scale sound, inevitably, is low frequencies. And the only way to improve low frequency response with a small speaker and a limited power source is to mess with the enclosure.
Small speakers that aim for good sound are always ported--they have a small hole with some kind of tube in it. The tube is of a diameter and length designed to resonate at certain frequencies. Check it out, you'll see what I mean. Any small radio that ams for decent sound, like, say, a Koss Mode1, will have a port in it. Your stereo speakers are ported. Cover the port and you'll heae the difference. I've not tried this yet, but I think the best way to improve sound in, say, and aristo steam tender would be to drill a hole and put a 1x1 or 1x2 length of PVC pipe in the hole.
If I wanted to make a big impressive looking magnet I would just use a less powerful magnet that was phyically bigger. Alnico magnets on guitar and bass speakers in the 50s were huge. "Ceramic" magnets were smaller. Neodymium magnets are tiny and weigh very little but have the same flux rating as magnet four times their size. It's not the size of the magnet that matters here.