There will always be minor sonic differences when hooking different gear together, with quality gear the differences are rarely night and day, more on the subtle side, in my experience.
If you have more digital sources you want to connect (PC, Disc Player, Streamer, etc..) you may want an external DAC and amp or an all in one amp/dac.
If you exclusively use your V40 and just want more flexibility/power for your headphones then pick up an amp and skip the DAC.
Gain: The 1x and 3.3x gain is best if you have easy to power IEM's or earphones. If all you have is full size higher impedance headphones and you listen loudly then go for 2.5 and 6.5x.