As for dimensions, the receiver is 17.1 inches wide, almost 6 inches high, and 14.75 inches deep, and it weighs a modest 21.2 pounds. As is the case with many A/V receivers, this model's amplifiers generate a fair amount of heat, so make sure to provide adequate ventilation.
A smattering of front-panel controls give you instant access to key functions and inputs, and the front-panel display is easy enough to navigate. But you'll be spending most of your time with the TX-SR504's partially backlit remote, which is a model of efficient layout and design. It makes it easy to adjust each speaker channel or the subwoofer without delving into the receiver's setup mode. A press of the CinemaFilter button gently smoothes the sound of overly bright or harsh DVDs, and the Late Night function can reduce the dynamic range of movies by automatically raising the apparent volume of quieter scenes and lowering the volume of loud sounds. We found the two features highly effective and potentially useful. The Onkyo TX-SR504 is rated at 75 watts per channel and offers the usual bevy of Dolby and DTS surround modes plus Neural Surround, which is used to decode XM's HD Surround channels. To receive XM's 160-plus music, talk, and entertainment channels you'll need to purchase a Connect and Play antenna (such as the Audiovox CNP1000) or a newer XM Pass kit, plus an XM subscription.
We like that the TX-SR504 offers an unusually wide range of crossover settings including 40Hz, 50Hz, 60Hz, 80Hz, 100Hz, 120Hz, 150Hz, and 200Hz. With so many options, you can dial in just the right crossover to produce seamless integration with any size satellite and subwoofer. Oh, and the menu offers a Double Bass setting that ensures bass signals will always be sent to the subwoofer, regardless of speaker settings--many receivers lack this feature. The Onkyo also has front-panel-mounted bass and treble controls.
Around back you'll find three A/V inputs, each of which can accept composite, S-Video, or component-video connections, while a fourth composite-only A/V input is located on the front panel. The TX-SR504 doesn't offer HDMI-switching as some more expensive midrange AV receivers now do, but it does have component-video switching. This allows you to connect as many as three different devices (DVD player/recorder, HD cable/satellite box, gaming console, and so forth) and conveniently switch between them with a single output to your HDTV. This comes in particularly handy when your TV only offers two--or even a single--component-video input. Unfortunately, the TX-SR504 doesn't convert composite or S-Video sources (such as a VCR) to component video. For that option, you'll have to step up to the Onkyo TX-SR574 ($399 list), which is also slightly more powerful (80 watts per channel).
On the audio front, you get four digital audio inputs--one coaxial and three optical--but no digital outputs, which is small bummer. The 7.1-channel analog inputs will be very useful when hooking up Blu-ray, HD-DVD, or SACD/DVD-Audio players, and there's also two pairs of stereo analog audio-only inputs--one with a Tape Out loop for recorders. You'll use the subwoofer output jack to connect a powered sub, and the unit's high-quality speaker binding posts accept bare wire ends or banana plugs. If you're connecting an extra set of stereo speakers that live in another room, it's worth noting that the B speakers' spring-clip connectors work only with bare wire ends. And lastly, if you're interested in a more integrated iPod solution, Onkyo's nifty but somewhat expensive DS-A1 ($100) iPod dock connects to the RI (remote interactive) jack.