Commcat's recommendation is bang on - see my virtual system for an alternative to a bookcase. The other issue is quarter wave cancellation in the bass from the wall behind the speakers. As the article explains, the only way to eliminate this entirely is to go to a soffit mount (as they almost always do in high end studios with their main monitors). An alterntive is to add plenty of bass trapping on both walls but at these frequencies you will probably need at least 4 GIK tri-traps or something of similar size before you can begin to make a difference.
Unfortunately a TACT or a PARC or an PEQ is unable to fix nulls (unless it alters the phase - which some EQ's do and which you might not want if you have phase accurate speakers to begin with). However, since a TACT or PARC allows you to EQ down the peaks then generally the "nulls" are much less masked by the peaks - so it really helps. Another trick is to have copious bass (more than you need) and then EQ the peaks down to get a desired response by attacking ONLY the peaks.
The unfortunate thing about nulls is that you cannot boost them or fix them in any other way except for speaker/listener placement and room acoustic design/treatment (if you wish to avoid playing with the phase of your bass signal which may affect how you perceive transients). The bad news is that this takes tremendous amounts of absorption to achieve - huge huge booskhelves and other large thick absorbers that work at bass frequencies. You can achieve good results with helmholtz tuned devices (like tube traps) but ONLY if you really know what you are doing - I'd suggest you hire an acoustician like Rives in this case - broadband bass and lower mid absorbers are easy for anyone to add to room corners and can really only do good....resonators require much greater expertise, IMHO.
What you have discovered is a common problem for 90%+ of all HT and full range two channel listeners. Most people focus on ever higher end more expensive gear and simply ignore this issue altogether and contend that it does not exist. These are mostly cases of extreme wishful thinking, where WAF or room aesthetic issues have a much higher priority than good sound.
Unfortunately a TACT or a PARC or an PEQ is unable to fix nulls (unless it alters the phase - which some EQ's do and which you might not want if you have phase accurate speakers to begin with). However, since a TACT or PARC allows you to EQ down the peaks then generally the "nulls" are much less masked by the peaks - so it really helps. Another trick is to have copious bass (more than you need) and then EQ the peaks down to get a desired response by attacking ONLY the peaks.
The unfortunate thing about nulls is that you cannot boost them or fix them in any other way except for speaker/listener placement and room acoustic design/treatment (if you wish to avoid playing with the phase of your bass signal which may affect how you perceive transients). The bad news is that this takes tremendous amounts of absorption to achieve - huge huge booskhelves and other large thick absorbers that work at bass frequencies. You can achieve good results with helmholtz tuned devices (like tube traps) but ONLY if you really know what you are doing - I'd suggest you hire an acoustician like Rives in this case - broadband bass and lower mid absorbers are easy for anyone to add to room corners and can really only do good....resonators require much greater expertise, IMHO.
What you have discovered is a common problem for 90%+ of all HT and full range two channel listeners. Most people focus on ever higher end more expensive gear and simply ignore this issue altogether and contend that it does not exist. These are mostly cases of extreme wishful thinking, where WAF or room aesthetic issues have a much higher priority than good sound.