For a long time Ive been using an original Behringer MDX in de inserts of my 2 channel bass input module, but I like an open top-end and the MDX adds a lot of hiss, which is not the most practical combination, of course. I dont mean that it amplifies hiss coming from the instruments. With nothing plugged in, the MDX is completely silent when bypassed, but adds serious hiss when processing is turned on, so this hiss must be created by the MDX's circuitry itself, since there is no source of hiss going into the compressors.
But its an old unit, its time for something new.
I use 2 compression stages in my signal chain and the one at this position is mainly used to prevent a too big volume boost going into the preamp, increasing the amount of drive and overal volume too much, when I turn up the mid EQ on my bass. With the mid EQ I want to color the sound, not increase overal volume a whole lot. A bit further on in the chain is a 2nd compressor to provide extra punch, so the main objective of the 2 channel compressor is keeping signal levels in check, not punching up the bass sound. Although I dont see extra punch as a bad thing ;)
Could someone advise me on a 2 channel (preferably rack-mountable) compressor, that works well for bass, that doesnt add annoying levels of hiss to the signal? Looking at current prices, I wasnt thinking around up to a couple of 100 bucks, but if the unit I need costs more to do the job right... so be it.

I’ve got a Composer Pro MDX2600, never had noise issues with it, in fact, it’s like it’s not in the signal chain, it’s very transparent for its price.
Have you compared it with something else? just to make sure it isn’t faulty, you have two stages of compression, which will bring up noise in the system, I’d check the MDX and substitute it for something else if possible, before spending any more money at all.
Spending 200 bucks won’t get you anything significantly "better" than the MDX, lots of people use these because they are cheap work horses that perform well for the money, I guess you know all this, but I’d check out a few things before coming to any conclusions just yet.

Perhaps the inserts on the bass module are designed for pedals rather than line level?
What is the model of the bass module and what settings do have on the controls of the Behringer?

What bass and amp do you use?

I like compression on bass and eventually settled on a Wampler Ego Compressor I had found too polite on guitar but was just the thing for bass....

I tried the 2 channel compressor in the effects loop but it never seemed to work for me.

All depends on what you are wanting to achieve - I have a P Bass and go for a rounded rather than modern sound so if you want that mid boost thing from an active (?) bass that will be a different result to achieve. However, if you can maybe consider spliting the signal and having one amp for a clean deep sound and the other for any grunge and feature effects....

Not an expert at all, but I´ve always read good reviews and comments about how transparent the FMR RNC is, and I eventually bought one three years ago that I seldom use since I´m all ITB, basically. But I can testify that it´s very transparent and versatile. I´ve tested it on bass, vocals, drums and guitars, and it´s very easy to work with (and very easy to overdo, since it´s so transparent, especially when the "Super Nice" mode is engaged...)

There's the ubiquitous dbx 166XL for cheap and cheerful or the ART PRO VLA II at your price point.