Need help ! Looking for a low cost integrated tube amp for my office


Looking to upgrade my office system
Music playing through my computer to an Audio engine D1 DAC
At present an old NAD receiver playing to four Vienna acoustics Haydn Grand book shelf speakers and a velodyne sub
Thought I would try my first experience with a tube integrated amp 
Any suggestions ?
fullerco
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I'm using a Mystere IA-11 integrated amp w/ 40 wpc. It is meticulously built by sister company Primaluna and is on sale at Up Scale Audio. It uses high quality parts and even a ladder resistor volume control instead of a potentiometer. Sound is clean and articulate w/ tight bass, tubey midrange, and extended highs.

http://www.mystere-eu.com/usermanuals/mystere_manual_ia11.pdf
Would you want to power all 4 speakers and the sub with the integrated? If so, you're going to be hard pressed to find a low cost tube integrated with more than two sets of binding posts, much less a sub out. Have you checked into an upgraded NAD?
sub has its own amp, thought this could be my tube opportunity. Would like to have all four working.