Either of these will work great with your A38 (especially if you're adding another), but as mentioned, I would also try the PMC Twenty series too. All very different sounding, so an audition is essential. The GX300 will give you more of what you're used to, but is quite a jump up in terms of quality and capability. Much more refined, a bit smoother, but still not too smooth, despite the ribbon tweeter. I find the GX range the most balanced range that MA have produced so far.
The KEFs will be smoother, and better integrated across the frequency range, in my opinion, and sound cleaner due to very little cabinet colouration. The PMC's will be a little leaner sounding, reminding me more of a sealed cabinet in presentation. They do allow quite an insight into the music though (the only way I can think of describing it), being able to hear layers even in music that isn't particularly well recorded.
But as always, its subjective, so you may find different results