Mid-fi integrated tube amp advice

Perhaps start with a hybrid?  This one is well regarded and I can speak from experience that it is a nice unit at that price:

https://www.audiogon.com/listings/lis8gbgh-unison-research-unico-nuovo-amplifier-hybrid-tube-integra...

Another option that is full tube with built in phono and dac:

http://www.usaudiomart.com/details/649421814-ifi-audioretro-stereo-50el84-tube-integrated-amplifierd...

Also check out the Yaqin integrateds, but stay away from the hybrid designs.

The unit you linked would worry me about quality due to the built in 'meter tubes' on the ends.  I've never heard of the brand which gives me more pause as well.  The products listed above are much better choices - I'd probably go Unison, then Yaqin, then iFi as the iFi might be just a little shy of power for those q900.

be wary of cheap imports, 

you can drive your speakers with 15 watts of tube power

look at a good used Primaluna PL1 or 2.  around your budget. i had one for 6 years. great amp

Not mid-fi (much better), but check out the Unision Unico

https://www.audiogon.com/listings/lis8gbgh-unison-research-unico-nuovo-amplifier-hybrid-tube-integra...

Earlier models were 6 Moons integrated amp of the year, Stereophile Class B.  I love mine.  Mine is 15 yrs old.  I am second owner and have had it now for 8 yrs.  Was thinking of replacing it last year just because of age, but it is such a wonderful integrated amp that instead I had it modded by Underwood Hi-Fi.  Hopefully it will serve me well for the next 15 yrs or more.  A really under appreciated amp!