I'm using the ecc99 in the input stage. 5687 is very nice too. Also tried the 6N30P but did not like them very much in this position.
Never tried a DHT but went on to build a Karna instead. I picked the AVVT 8B as a driver but with the increased gain and double the filament voltage compared to a 45, I could not get away with AC on the filaments. I think you will experience the same with a EML 20 + you have to deal with microphonics. But it could be a very nice amp if you manage to get it right!