Hello
Yes you can. You can connect any source via Rca to any amplifier.
You can also use a 3.5 mm plug with an Rca connector at the other end and connect your tablet/smartphone.
What may not have been mentioned is that a good tube for the Dark voice can cost a lot of money if you want a good one.
The ones for the Little Dot are a bit cheaper and easier to find.
And the tubes of the Little Dot are somewhat better than those of the Dark voice as standard.
The workmanship is also better.
I can’t say anything about the Battle amp.
There was only one measurement on Asr that was a bit strange.
I can only say that I have the Little Dot 1+ and it is relatively good with a good tube set. The Mk 2 is the successor of the 1+ which has been improved again.
And the Mk 3 has been redeveloped.
The Little Dot is better in terms of workmanship and the choice of parts used.
The Dark voice is and will be “officially” hyped.
Maybe you should take a look at the bad sides of the amplifiers and see if that helps you in your choice. 