I believe the difficulty of the Tungstens to drive is somewhat exaggerated. Pretty much any decent amp can drive them fine, even something weak and cheap like a darkvoice. The issue is volume. Most difficult to drive headphones are difficult to drive because they require a lot of current. The Tungsten is not difficult to drive for that reason, but because of voltage. Most amps output 10 volts, though some output 20 volts. 10 volts is enough to get the Tungsten above 100 decibels, while 20 volts is enough to get it above 110 decibels. Because volume is logarithmic, the difference between 100 and 110 is massive, not just a 10% increase. But download a sound level check app and see how loud your music is. Most don't listen above 90 decibels ever. I listen to super loud rock and metal, and rarely get above 103 decibels. The point is just about any half decent amp can drive it fine, it just might be preferable to have one of the select few amps that put out 20 volts, at least if you listen super loud. Premium amps like the Bliss and Oor can do that. But even the $400 Topping A70 Pro can do it also. The DS is actually a little easier to drive than the SS (the volume is a little higher at a given voltage). All the more reason to go with the DS, unless saving the $500 is important, or you perfer the more v shaped tunning. More voltage isn't better, as long as you get it to the volume you want. The CFA3 is one of the few amps that output 30 volts (which only gets you from about 112 decibles to 115 decibles compared to 20 volts). Apart from the fact that these volume levels will quickly damage your hearing and so no one should be listening this loud, I talked to Goldensound at canjam and he perfers other amps, like the Bliss and HM1 (which only outputs 10 volts, and which he uses to listen to the Tungsten, which is one of his favorite headphones) to the CFA3. He thinks they are just better amps, desite the voltage difference. My point is, as long as your current amp can get it loud enough, and this is pretty easy to determine (based on its voltage and your listening volume), your current amp is probably fine for the Tungsten. If it can't, there are cheap amps you can get that will get it loud enough (the topping A70 pro or speaker amps for example). Here is a technical discussion from Goldensound on this:
https://forum.headphones.com/t/modhouse-tungsten-measurements-official-discussion/22645/36?u=resolve