Admittedly a bit lost

I would go to as many dealers as you can to get a flavor of the speakers that sound good to you. You will need to determine if you want stand mounted or floor standing models. When you can narrow it down it would also be a good idea to bring your amp to the dealer for a demo. This can be a bit overwhelming, but trust your ears for a speaker that sounds musical to you with various types of music.

What about the Q Acoustics speakers?

Go on your local Craigslist and pick up a pair of Klipsch Heresy’s or Quartet’s. Few hundred bucks. You can always unload these. If this is your first pair of high(ish) end speakers, buy used. Also, never buy speakers without auditioning first.

Like Whart, with whom I agree, I believe you have some fundamental limitations in space and volume levels permissible, which will to a great degree dictate the equipment (in this case speakers) you will be able to use.

You don't want large bassy/boomy speakers. In fact speakers with a early roll off of bass, say below 60hz might be a good thing. Keeping smallish speakers off the floor on stands (no floorstanders perhaps) might also be a good thing to limit the transmission of 'thump, thump, sounds to your neighbor.

Another limitation in choices is that you will want to choose a speaker which sounds linear (especially in the bass) at low volume levels a reasearch project in itself. A lot of speakers only sound alive at medium to high volume levels (that is why the early audio gods created tone controls in their pre-amps etc, so you could boost the bass a tad, or provided a loudness contour).

I hope that helps you to focus a bit. But it is a pretty steep learning curve so take your time making decisions. FWIW I don't really believe in making decisions based on dealer demos with different equipment in different rooms. It will always be different when you get it home. So unless you know what you are chasing down you are likely to make some poor decisions (learn all you can about each products design, performance, synergistic equipment, etc. before you get caught up in the web.

Hope that helps a bit, but I think it is premature for me to be making recomendations. BTW, I think you should be able to match a pretty good speaker to your Jolida.

Good luck.

I can tell you what I listen to without recommending you follow exactly the same path. I also have a 38 watt tube amp. In my home, I use speakers with Fostex drivers and dual 8in subs run in parallel. These will address your mid range preference and provide separately adjustable bass with a driver fast enough to keep up and deep enough to sometimes feel the bass without shaking the building you live in at moderate volumes.

You might need a powered subwoofer to get the bass right.
Something like REL.

You wrote: "With those constraints, my dilemma is that I don't know if I
should be trying out high-efficiency speakers or low-efficiency ones? Should I
look for 8ohm speakers or 4ohm ones? Something tells me that with low power
tube amps, I should be looking at a high efficiency low impedence speaker.
However, will that sort of speaker be able to navigate the high speed bass attack
of electronic music when driven by an amplifier such as mine?"

As Whart suggests, listen to as many different types/brands of speakers as you
can but in response to your "intuition" above, I'd suggest higher
impedance speakers (8 ohm preferably, 6 ohm min.) rather than low. I'm
guessing you're talking about an integrated amp (JoLida 202B??). Drag your
JoLida along with you if at all possible when auditioning. I also suspect for your
electronica and deep bass music you'll want an efficient design to get the most
out of those 40 wpc.

[Had a JoLida 502B for years...really enjoyed it.]

Is the Jolida just a power amp or is it integrated? If not, what are you using for a preamp? Also, what is your source?

You are likely to get all kinds of suggestions regarding equipment, brands and the like- I'm less inclined to offer that, and to suggest some methods to approach this.
First, be careful what you wish for- low bass, particularly of the synth variety, and apartment living, can be challenging. I guess you want something that can play deeply and clearly without being too loud, but before you start dumping money into gear, I think you need to determine what will set your neighbors off. Wonder if any dealer (or electronics geek) with the ability to run some kind of sweep tone through amplification can help. (Do you play and have a synth and instrument amps? That could be telling, and you may already know the answer).
Second, the amp-speaker relationship is critical, but I wouldn't center my decision on finding a speaker that works well with that amp- you could and should listen to a variety of speakers and then determine what best matches your needs. I don't know the current Jolida line (certainly heard of the brand), but worst case, you could sell or trade the amp to optimize the speaker-amp relationship. Am I saying that the speaker is the most important? No. But the relationship between the speaker and amp is critical and you are already limiting yourself by confining the universe to those speakers that will work well with that amp.
Third, the biggest limitation is probably the dealers themselves. Even if you live in a large metro area, it is tough to listen to, let alone compare, various brands on the same system, in the same room. If you are located in a less audio gear-centric city, the challenges are multiplied.
There's lots to learn about impedance, amp performance and efficiency (people can argue endlessly about what works best), but the final arbiter will be your ears. There are folks that have used relatively low powered tube amps with speakers that are not supposed to be friendly with tubes or low power and others who use high powered solid state amps with horns, when a few watts will suffice.
Is there an audio club in your city? It is a good way to get to hear gear in a home environment without the limitations and agenda that may be operative at a retailer. (Not all dealers are bad, but finding a good one you can work with is not easy, even when spending mega-bucks).
A couple other random thoughts- buy Jim Smith's book, it is called something like 'Better Sound.' It's all about how systems get set up and tuned for the room. (Jim does private consultations to voice systems, and much of what is in his book is basic knowledge, but may prove helpful). The room is a big part of the equation.
One other thought - and I am treading into 'gear' suggestions here, but I'll take the risk. I have been using horns after decades of electrostatic speaker use. The can give you the punch and jump, the bass can be trickier and making it cohere with the upper ranges is often difficult. But one sort of bargain is certain lower priced JBL horn arrays that are not marketed to hi-fi cognoscenti. These may float your boat, and may be OK with the Jolida. They are typically discounted new, and while not "audiophile approved" can probably deliver much of what you want at a reasonable price. (The company's upper priced stuff is marvelous sounding, despite the "branding" as a commercial/industrial product). Good luck, and make it an adventure rather than a frustration. I'm sure you will get many product suggestions from others- many of which may be worth exploring. But, in the final analysis, you have to be pleased- and that's hard to judge in limited showroom listening sessions that have many uncontrolled variables in system and room. If you do visit dealers, my suggestion is to make appointments in advance, and bring some of your own source material- of different types, to reveal the full range of a given set-ups' performance.