Your comments give us an opportunity to explore the differences between the Swan D2.1se and D1.1se, sterryo. When comparing a fresh pair of Swan D1.1se to a seasoned pair of D2.1se there are at least three things to keep in mind.
The first is that a pair of "green" speakers - especially those with the relatively high mechanical losses these particular designs need in order to hit their design centers - need to be well broken in before critical evaluations. I wouldn't expect to do any comparisons until either model had acclimated for a few days and had been run and heat-cycled for up to a hundred hours. I don't know what vintage your D2.1se are, but it's clear they've been run long enough to settle in at their design center.
The midwoofers in both of the D series speakers you have use high-loss suspensions, meaning that the driver's compliance factors more into the system tuning than usual. Had the driver been designed and engineered with low-loss suspensions that rely more heavily on the motor controlling the diaphragm this would be less of a factor. (For example, our upcoming new Dana models are all low mechanical loss designs and you'll notice it immediately in the softness of the driver's outer suspensions.) Gently prod the D1.1se's rubber surround with a finger and you'll see what I mean - behind the cone there's a rear suspension that's just as stiff. You really have to exercise the suspensions in the D series in order to get the speakers to "bloom". Further, even the electrical components inside need to be formed, and this also requires quite a few cycles at fairly high currents to accomplish. Basically, play 'em fairly loud for a long time and then listen again.
Second and just as importantly, the D2.1se and D1.1se occupy decidedly different acoustical classes. As you've found, the D2.1se is designed as a powerful main "stand monitor" loudspeaker. It benefits from free-space use and will probably not be happy where the D1.1se would be best used, which is with some boundary assist. Conversely, the D1.1se, while similar in components and tuning above the middle hundreds of cycles, benefits from boundary loading in order to resemble the D2.1se's sound from free space. I think TAI can best describe the D1.1se as a bookshelf or minimonitor loudspeaker that when combined with the D2.1se stand monitor in a multi-channel system, is best nearer to a large boundary. Knowing that this was where and how most D1.1se's would be used, Swan dialed in a touch more high end in the D1.1se to balance what might be a number of decibels down low added by boundary gain.
This characteristic also makes the D1.1se suitable for relatively densely packed wall units and entertainment centers and/or used with a subwoofer set to cross it over nearly a full octave higher than the more full-bodied and much larger D2.1se. The D2.1se is a fourteen liter system and the D1.1se is only a five liter system. They share bass driver motors and tweeters, meaning that most of the parametric difference between the two speakers will show up in the F3 and less so in their relative sensitivities and overall responses. For this reason you cannot substitute one model for the other either in space or in the other's active filter setup and expect immediate success. Ideally any main speaker should be set to add its natural highpass function, including slope and frequency, to an electronic function that sums with it to mirror the subwoofer's lowpass 4th order, Q=0.5 function at that same frequency.
Lastly, you'll need to acclimate yourself to these differences, sterryo. Even without the important factors above, if you've spent a couple of years drinking a mature Shiraz, suddenly switching to a new Pinot Noir will give a sense of vivid, pronounced change. Give yourself some time to mentally settle both flavors, and experiment with pairing them with more suitable dishes - use the two different models in their optimum settings, carefully arrange your positioning and your electronic crossover settings in your AVR to suit each, and once you've passed break in, you should be loving things.
Following are the acoustic models for each model, plus for fun, the D2.1se Custom's response. Note that all are virtually identical in loudness but that the F3 vary noticeably, and in the case of the D1.1se, significantly. This is what the same motor driving an alignment less than half the size of the larger models looks like. In order, D1.1se, D2.1se, D2.1se Custom.
In summary, break them in, use them in their respective design spaces, and acclimate. Remember that there is a theoretical difference between full space loading and half space loading of six decibels, which is a phenomenal amount of level difference, some or most of which will factor in any room. We anticipated a degree of this when we designed both models and we'd be the first to agree that while the similarity in their crossovers means the D1.1se isn't bright, it's much more suitable for half space loading than the D2.1se. Neither will sound like the other if they're simply substituted back and forth in the same setting, especially fresh out of the box.
It's also possible your system is on the lean side, which when paired with a robust fullrange sound like the D2.1se, by comparison highlights the D1.1se's missing bass octave even more when you make such an abrupt switch without including these other factors. The latter is only a little over half the cone area and less than half the former's air volume. It's going to be a significant difference even without factoring break in, setups, and rooms.
If you want to delve more into this, I'd encourage you to call us and I'm sure we can walk you through it. Speakers of this class and performance level are sensitive to literally everything in the system and the room and it's partly a testimony to that ability that defines these models. The mark of a high definition loudspeaker is its ability to report back to you those factors and more and I think that with the D1.1se, Swan developed a unique solution for high definition multi-channel and multi-use that does that.