Room EQ and room tuning in general can be quite challenging. It can be very interactive, iterative, and a good deal of "technique" is involved in getting good measurements as well as generating a resulting EQ filter set.
What I'm hearing here is that you've tried two of the premier measurement and EQ systems and didn't like the results. I certainly understand your reservations in buying hardware when your software-only efforts have fallen short. I can't think of a good reason why dedicated hardware DSP would be radically different from your software implementation either.
After years of calibrating rooms for people I've found three general reasons why the results are not perceived as an improvement:
1. Measurements not properly taken, so the resulting EQ is not correct
2. Auto EQ system fails because required correction is "out of range" (I've found this with both Audyssey and REW-generated filters, but at least with REW you can make changes that get better results, with Audyssey you're kind of stuck with it).
3. The pre-EQ sound quality has become "accepted" as normal, so even if the post-EQ version is technically improved, it's different, and therefore not viewed as an improvement.
I'm a little concerned that you generated a "Parabolic EQ Filter", when you should have generated a set of parametric filters (it's almost never just one), but I don't know what you've done or how you've done it, and I'm not about to coach here. Suffice it to say that many people trying Room EQ make similar errors, like using a single mic position, the wrong mic position, using an uncalibrated mic, not verifying the results (other than listening), and a host of others. I'm not saying you've done any of this, just that there are many common user errors to consider. Measurement quality is where most of the variables are.
Most of the work in getting room EQ to function optimally is on the measurement side, followed closely in the case of REW by interacting with the Filter Tasks settings, iteratively, to optimize the resulting curve. In the case of Audyssey MultEQ XT 32 with the Pro kit, there are also some optimization tasks to work with once good measurements are collected. Then, verify the result regardless of what system is used, again, using the proper measurement techniques. It's not at all unusual to find the result is other than what is expected or desired.
Don't be too quick to give up. Professionals who equalize commercial cinemas and dubbing stages with Dolby equipment have to make several attempts at manual EQ before it all settles in. And yes, they verify too!