Help!!!

Wife and I want to add the Buck 91 wood burning insert to my fireplace but have a problem.

The fireplace is in a family room finished basement of a single story ranch. The chimney is approximately 20 feet high. We have a double fireplace with one upstairs and they have separate flues.
We have a very low pressure and poor drafting in the basement. We tried an insert before (slammer install) and had fairly significant smoke and fume problems.

The downstairs flue is offset from the chimney by about 3 feet to the right. We had a guy that came out and says he can't install a liner like that and to consult a sweep or someone more knowledgeable
about that type of connection. I'm suspecting this is the culprit to our poor drafting.

Can a SS liner be installed like this? If so, how hard would it be to clean with an angle like that? Any concerns?

Thanks in advance for any advice we can get.

How much would cracking a window help with the pressure?

I'm assuming I have a pressure problem, house is highly insulated. Any way to determine pressure level?

So a lazy draft would definitely be a low pressure problem then?

I was thinking because the chimney is offset so far from the flue (about 3 feet) that it was
the main problem in it not venting very well.

Strange thing is when I burned wood directly on the grate the draft didn't seem to be real bad,
but with the now removed Appalachian 36BW (which was just slid in slammer style I believe) we
had a fairly significant amount of smoke when reloading the box.

I have another company coming Friday to take a look at it.

I was going with the low pressure theory as I've read where basement fireplaces in well insulated homes
have that problem.

Any way to test the pressure?