I actually own a Trends. It is an excellent little amp. I thought Trends was coming out with a DAC as well, no?
You are completely correct about the USB feature on the AE. Good only for printers. So, you've got to get a DAC with an optical toslink input. There is a lot of debate about USB versus optical, but don't bother reading it. Plug, play and enjoy the music, both sources are excellent. You will be using optical.
The next debate is about optical/toslink cables. Some claim glass optics deliver a better sound...as I say, optical delivers only light...on or off. There's no way to improve that delivery so don't buy expensive cables. I will say that the cheapest cables are flimsy and will fail if stressed (i.e. bending at acute angles, etc.) so get a well made cable, just not one that boasts better quality sound for outrageous prices. Check out the "pro" toslink cables on ebay.
As for DACs. Once again, plenty of hot air out there, but the bottom line is that if you get a DAC with the latest 24bit/192khz chip technology and really low distortion, you should have a transparent device, meaning data is exchanged without corruption or coloration.
The best long-term solution for you is the new Benchmark Media Pre. http://www.benchmarkmedia.com/dac1pre/
It will serve as your DAC and pre-amp to the Trends (which you can disable its pre-amp control). It also has multiple inputs and an excellent headphone amp. You would never have to buy another DAC or preamp. If you want to spend half its price, buy a used Benchmark DAC-1 on Audiogon, it's still around $700, but a great investment.
You already have a very transparent amp in the Trends, so the information will arrive at your speakers unmolested. The speakers are the most subjective aspect of your system and will alter the sound dramatically depending on which you use. Therefore, choose wisely! My suggestion? Barring exotic formats like open-baffle (which I prefer) a really nice used pair of ADS speakers from the 80's can't be beat (and for not much money). These speakers reward me every single day.
Good luck out there! Don't let the whack-o audiophiles drag you into the murky waters.