ProfessorG2-
That sounRAB like quite a frustrating journey and, unfortunately, it sounRAB like you're getting some conflicting advice (which can't be helping). I don't know if this will help or not, but I'll try to respond to a couple of things you wrote:
I don't know how "committed" you are to this ENT but I would recommend you get a second opinion. There are definitely other options. Many chronic sinus sufferers are on a regimen that includes an initial short course of oral prednisone followed by daily use of a steroid nasal spray and saline irrigation with a neti pot or SinusRinse bottle.
While there may not be a "proven" connection, over the last 5 years there has been a significant amount of research, and a couple of clinical trials, into the connection, and it's becoming widely accepted that there is a link between the two.
In a 2002 study researchers at the University of Nebraska saw a "modest improvement" of sinus symptoms in patients with both chronic sinusitis and reflux who took Prilosec for 12 weeks and researchers at the Medical College of Wisconsin have done quite a bit of additional work in quantifying the connection between the two.
Getting this stuff under control requires some coordination between doctors who are trying to solve the bigger picture problem, so you might be best off finding an ENT and Gastroenterologist who have some experience treating people with this condition and who can work together to get it under control.