Retrofit Volvo V60 B&W

[mrs]

According to this, XC40 only has 1 speaker on the front doors. There is no place for additional speakers! On the other hand it has two speakers on the rear door.  
If you do not have the roof speakers already, most likely; you won't have the wiring too. 
I don't want to discourage you but it won't be easy to find used parts because not many people has XC40 with H&K or B&W and they are not the same speakers as 60 and 90 series. 
So, my advise to you start from the basics before even trying to finds the parts.  
From the Orbit, enable the SUB and just connect a speaker to the AMP.  "You can push wires into terminal holes" and check if you even get an output from your existing AMP (AUD) with its current config software. 
Not sure if your basic AUD "No SUB" has center (Dash) and roof outputs but you can test same way as the SUB.

Today i checked what have in my car, below link with pictures from car,

https://mega.nz/folder/nxdVUTxB#l3XxC05fXGRhCgNnX1ykwA

so as i could conclude, 2x speakers in front doors - left+right, 4x speakers in rear doors - left+right (top and bottom of doors) , even for me strange at rear doors is there at the top of doors 1 or 2 speakers in his long trim, if we say 1x, then its in total 6 speakers + 1x speaker in dashboard = 7 speakers

So, in total 7 speakers + AMP under passenger seat, you can it on photos, with as could see 4 connectors, but difficult access it without desoldering for detailed check.  And saw these  2 location on rear part of car, not sure what they are and are those places where will be added some speakers...

At the roof no speakers.

Hm, not sure is difficult find XC40 HK speakers, as here in Europe could see at ebay more guys sell full set of HK XC40 speakers, full set price 700 to 1k euros, and even out of ebay can find it at many local selling websites in different EU countries, as for me not big deal order from any EU country,

https://www.ebay.com/sch/i.html?_from=R4...n&_sacat=0

checking prices from your links, seems in USA not so bad prices, even for new speakers ,  maybe will ask some friends from USA to order it for me there .

Clear about testing AMP (AUD) ,  think no problem about output for dash speaker, as in car is already dash speaker, roof speaker is missing.

Will i need replace AMP-amplifier, those you call aud, if change speakers to HK?