Frim Bike Radar: "The Attain Pro is built around a 68mm BSA threaded bottom bracket"
If you put a MTB crankset on this bike, regardless of where you put spacers, you will screwup the chainline, which will screw up the shifting...

It's not just the BB width but also the additive factor of width of MTB cranks...
Use a road crankset... add a cassette which starts with larger cogs - Miche makes cassettes which start with 14 or 16 and 18 , in 9 speed for Shimano compatible shifting. (also have cassettes for Campy compatible). Miche makes great cassettes, Italian company, also available in US and most anywhere...
You might also be able to try a Gravel Crankset which goes lower (46/30) than common road of 48/32, if you don't like the road range...
Just get a cassette which can work with your desires.
Gravel Cranksets will be 2mm wider chainline for a 68mm BB, which would still work...

... mtb BB and crankset on a road bike... is a serious Kludge ...